how to populate a datagridview based on selected row

I'm trying to populate a datagridview based on the selected row in another, as an object kind of.

public Form1()
{
     dg1.SelectionMode = DataGridViewSelectionMode.FullRowSelect;
     Allemployees(dg1);
}

The following function is returning all employees to the first dg

    private void Allemployees(DataGridView dg)
    {
        conn.Open();
        SqlCommand cmd = new SqlCommand("select * from emp", conn);
        SqlDataReader reader = cmd.ExecuteReader();
        DataTable table = new DataTable();
        table.Load(reader);
        dg.DataSource = table;
        conn.Close();
    }

How do i use selected row as an object and pass it to return emp_loc relations

 private void locsbyemp(DataGridView dg, int emp_id)
        {
            conn.Open();
            SqlCommand cmd = new SqlCommand(@"select loc_name From emp_locs WHERE emp_id = @emp", conn);
            cmd.Parameters.AddWithValue("@emp", emp_id);
            SqlDataReader reader = cmd.ExecuteReader();
            DataTable table = new DataTable();
            table.Load(reader);
            dg.DataSource = table;
            conn.Close();
        }

same thing with trying to populate "edit emp form" controls with selected row data

Thanks in advance