Google Cloud: How to list granted permission for user or service account?

If I understood your question correctly, you can see them in the "IAM & admin" console. In the "IAM" tab:

• With "View by: MEMBERS" option, you would be able to see a list of all members (users and services accounts) and the roles granted to them.
• In "View by: ROLES" there is a list of all roles and (if expanded) all users/service accounts that have that role.

In case you want to know more about those roles, in the "Roles" tab (inside "IAM & admin"), you can click on them and see exactly what permissions each one has.

Currently there is no gcloud command for listing all granted permissions as shown here, so I filed a public Feature Request on your behalf. Lastly, this is documentation for the gcloud iam commands.

If you feel like learning more about IAM, these is the overview and documentation for the product.

You can use Asset Search to find all the roles (not permissions) a user is granted with directly (not transitively) upon various resources within a given scope (i.e., an organization, folder, or project).

This allows you to search across projects and resources. However, you must have the cloudasset.assets.searchAllIamPolicies permission upon the scope.

Here is a sample command:

gcloud asset search-all-iam-policies --scope=organizations/123 --query="policy:foo@bar.com" | egrep "role:|resource:"

Documentation: https://cloud.google.com/asset-inventory/docs/searching-iam-policies

Supported resource types: https://cloud.google.com/asset-inventory/docs/supported-asset-types#searchable_asset_types

More details: How to list, find, or search iam policies across services (APIs), resource types, and projects in google cloud platform (GCP)?

You can use Policy Analyzer feature of the Cloud Asset Inventory.

Under the web UI there is a query template called "What access does my employee (or terminated employee) have?" that seems to fit your needs exactly.

See the official "Analyzing IAM policies" docs for more info.