How do I extract data from this http response?

As I understand your question, You want to access a data which you got from HTTP.

So,You can follow below steps.

To access data of empty_top_toolbar key

print("data" + message["RESPONSE"]["GenericListAnswer"]["empty_top_toolbar"].toString());

To access id of global_operation list...

ListView.builder(
   itemCount: message["RESPONSE"]["GenericListAnswer"].["global_operation"].length,
   builder:(context, index){
       return Text("Id ${message["RESPONSE"]["GenericListAnswer"]["global_operation"][index]["id"]}");
   }
)

Same way you can access key name.

First create a response model by converting json to dart model.

like have done this for given response data :

class ResponseModel {


RESPONSE? rESPONSE;

  ResponseModel({this.rESPONSE});

  ResponseModel.fromJson(Map<String, dynamic> json) {
    rESPONSE = json['RESPONSE'] != null
        ? new RESPONSE.fromJson(json['RESPONSE'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.rESPONSE != null) {
      data['RESPONSE'] = this.rESPONSE!.toJson();
    }
    return data;
  }
}

class RESPONSE {
  GenericListAnswer? genericListAnswer;

  RESPONSE({this.genericListAnswer});

  RESPONSE.fromJson(Map<String, dynamic> json) {
    genericListAnswer = json['GenericListAnswer'] != null
        ? new GenericListAnswer.fromJson(json['GenericListAnswer'])
        : null;
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.genericListAnswer != null) {
      data['GenericListAnswer'] = this.genericListAnswer!.toJson();
    }
    return data;
  }
}

class GenericListAnswer {
  String? emptyTopToolbar;
  String? noMoveColumns;
  String? noAddRemColumns;
  String? noSortColumns;
  String? noResizeColumns;
  String? noOperColumns;
  RefreshData? refreshData;
  String? noGuiLink;
  String? indexLast;
  String? maxNumRows;
  String? indexTrueLast;
  String? isHistory;
  String? indexFirstVisible;
  String? displayTableName;
  String? tableId;
  String? tableName;
  List<GlobalOperation>? globalOperation;
  String? numVisible;
  String? listType;
  String? listKey;
  String? parentClassId;
  String? parentCommonId;
  String? parentApplcolId;
  String? searchNum;
  String? idBoxSearchNum;
  String? madKeyList;
  String? chooseXsl;
  String? isSearchPopup;
  String? sectionListParams;
  QuickSearch? quickSearch;
  String? description;
  String? wfConfigured;
  String? opParameter;
  List<ListNode>? listNode;

  GenericListAnswer(
      {this.emptyTopToolbar,
      this.noMoveColumns,
      this.noAddRemColumns,
      this.noSortColumns,
      this.noResizeColumns,
      this.noOperColumns,
      this.refreshData,
      this.noGuiLink,
      this.indexLast,
      this.maxNumRows,
      this.indexTrueLast,
      this.isHistory,
      this.indexFirstVisible,
      this.displayTableName,
      this.tableId,
      this.tableName,
      this.globalOperation,
      this.numVisible,
      this.listType,
      this.listKey,
      this.parentClassId,
      this.parentCommonId,
      this.parentApplcolId,
      this.searchNum,
      this.idBoxSearchNum,
      this.madKeyList,
      this.chooseXsl,
      this.isSearchPopup,
      this.sectionListParams,
      this.quickSearch,
      this.description,
      this.wfConfigured,
      this.opParameter,
      this.listNode});

  GenericListAnswer.fromJson(Map<String, dynamic> json) {
    emptyTopToolbar = json['empty_top_toolbar'];
    noMoveColumns = json['no_move_columns'];
    noAddRemColumns = json['no_add_rem_columns'];
    noSortColumns = json['no_sort_columns'];
    noResizeColumns = json['no_resize_columns'];
    noOperColumns = json['no_oper_columns'];
    refreshData = json['refresh_data'] != null
        ? new RefreshData.fromJson(json['refresh_data'])
        : null;
    noGuiLink = json['no_gui_link'];
    indexLast = json['index_last'];
    maxNumRows = json['max_num_rows'];
    indexTrueLast = json['index_true_last'];
    isHistory = json['is_history'];
    indexFirstVisible = json['index_first_visible'];
    displayTableName = json['display_table_name'];
    tableId = json['table_id'];
    tableName = json['table_name'];
    if (json['global_operation'] != null) {
      globalOperation = <GlobalOperation>[];
      json['global_operation'].forEach((v) {
        globalOperation!.add(new GlobalOperation.fromJson(v));
      });
    }
    numVisible = json['num_visible'];
    listType = json['list_type'];
    listKey = json['list_key'];
    parentClassId = json['parent_Class_id'];
    parentCommonId = json['parent_common_id'];
    parentApplcolId = json['parent_applcol_id'];
    searchNum = json['search_num'];
    idBoxSearchNum = json['id_box_search_num'];
    madKeyList = json['mad_key_list'];
    chooseXsl = json['choose_xsl'];
    isSearchPopup = json['is_search_popup'];
    sectionListParams = json['section_list_params'];
    quickSearch = json['QuickSearch'] != null
        ? new QuickSearch.fromJson(json['QuickSearch'])
        : null;
    description = json['description'];
    wfConfigured = json['wf_configured'];
    opParameter = json['op_parameter'];
    if (json['ListNode'] != null) {
      listNode = <ListNode>[];
      json['ListNode'].forEach((v) {
        listNode!.add(new ListNode.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['empty_top_toolbar'] = this.emptyTopToolbar;
    data['no_move_columns'] = this.noMoveColumns;
    data['no_add_rem_columns'] = this.noAddRemColumns;
    data['no_sort_columns'] = this.noSortColumns;
    data['no_resize_columns'] = this.noResizeColumns;
    data['no_oper_columns'] = this.noOperColumns;
    if (this.refreshData != null) {
      data['refresh_data'] = this.refreshData!.toJson();
    }
    data['no_gui_link'] = this.noGuiLink;
    data['index_last'] = this.indexLast;
    data['max_num_rows'] = this.maxNumRows;
    data['index_true_last'] = this.indexTrueLast;
    data['is_history'] = this.isHistory;
    data['index_first_visible'] = this.indexFirstVisible;
    data['display_table_name'] = this.displayTableName;
    data['table_id'] = this.tableId;
    data['table_name'] = this.tableName;
    if (this.globalOperation != null) {
      data['global_operation'] =
          this.globalOperation!.map((v) => v.toJson()).toList();
    }
    data['num_visible'] = this.numVisible;
    data['list_type'] = this.listType;
    data['list_key'] = this.listKey;
    data['parent_Class_id'] = this.parentClassId;
    data['parent_common_id'] = this.parentCommonId;
    data['parent_applcol_id'] = this.parentApplcolId;
    data['search_num'] = this.searchNum;
    data['id_box_search_num'] = this.idBoxSearchNum;
    data['mad_key_list'] = this.madKeyList;
    data['choose_xsl'] = this.chooseXsl;
    data['is_search_popup'] = this.isSearchPopup;
    data['section_list_params'] = this.sectionListParams;
    if (this.quickSearch != null) {
      data['QuickSearch'] = this.quickSearch!.toJson();
    }
    data['description'] = this.description;
    data['wf_configured'] = this.wfConfigured;
    data['op_parameter'] = this.opParameter;
    if (this.listNode != null) {
      data['ListNode'] = this.listNode!.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class RefreshData {
  String? applEra;
  String? delay;

  RefreshData({this.applEra, this.delay});

  RefreshData.fromJson(Map<String, dynamic> json) {
    applEra = json['ApplEra'];
    delay = json['delay'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['ApplEra'] = this.applEra;
    data['delay'] = this.delay;
    return data;
  }
}

class GlobalOperation {
  String? id;
  String? key;
  String? only1;

  GlobalOperation({this.id, this.key, this.only1});

  GlobalOperation.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    key = json['key'];
    only1 = json['only1'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['key'] = this.key;
    data['only1'] = this.only1;
    return data;
  }
}

class QuickSearch {
  List<String>? quickSearchColumn;

  QuickSearch({this.quickSearchColumn});

  QuickSearch.fromJson(Map<String, dynamic> json) {
    quickSearchColumn = json['quick_search_column'].cast<String>();
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['quick_search_column'] = this.quickSearchColumn;
    return data;
  }
}

class ListNode {
  String? id;
  String? madKey;
  String? isCustom;
  String? isLocked;
  String? isInactive;
  RunHyperlink? runHyperlink;
  List<Field>? field;

  ListNode(
      {this.id,
      this.madKey,
      this.isCustom,
      this.isLocked,
      this.isInactive,
      this.runHyperlink,
      this.field});

  ListNode.fromJson(Map<String, dynamic> json) {
    id = json['id'];
    madKey = json['mad_key'];
    isCustom = json['is_custom'];
    isLocked = json['is_locked'];
    isInactive = json['is_inactive'];
    runHyperlink = json['run_hyperlink'] != null
        ? new RunHyperlink.fromJson(json['run_hyperlink'])
        : null;
    if (json['field'] != null) {
      field = <Field>[];
      json['field'].forEach((v) {
        field!.add(new Field.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['id'] = this.id;
    data['mad_key'] = this.madKey;
    data['is_custom'] = this.isCustom;
    data['is_locked'] = this.isLocked;
    data['is_inactive'] = this.isInactive;
    if (this.runHyperlink != null) {
      data['run_hyperlink'] = this.runHyperlink!.toJson();
    }
    if (this.field != null) {
      data['field'] = this.field!.map((v) => v.toJson()).toList();
    }
    return data;
  }
}

class RunHyperlink {
  String? classid;
  String? id;
  String? madKey;

  RunHyperlink({this.classid, this.id, this.madKey});

  RunHyperlink.fromJson(Map<String, dynamic> json) {
    classid = json['classid'];
    id = json['id'];
    madKey = json['mad_key'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['classid'] = this.classid;
    data['id'] = this.id;
    data['mad_key'] = this.madKey;
    return data;
  }
}

class Field {
  String? fieldName;
  String? colIndex;
  String? fieldValue;
  String? madKey;
  String? id;

  Field({this.fieldName, this.colIndex, this.fieldValue, this.madKey, this.id});

  Field.fromJson(Map<String, dynamic> json) {
    fieldName = json['field_name'];
    colIndex = json['col_index'];
    fieldValue = json['field_value'];
    madKey = json['mad_key'];
    id = json['id'];
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['field_name'] = this.fieldName;
    data['col_index'] = this.colIndex;
    data['field_value'] = this.fieldValue;
    data['mad_key'] = this.madKey;
    data['id'] = this.id;
    return data;
  }
}

now create instance of this class and get value from api response

ResponseModel responseModel = ResponseModel.fromjson(jsonEncode(response.body));

and now you can access which ever property you want using responseModel