Ag-Grid get Group column names

You can access event parameter whenever pivotMode is changed through columnPivotModeChanged. And you can also able to get RowGroupColumns by calling getRowGroupColumns() through columnApi in event parameter.

1. columnPivotModeChanged()

event: ColumnPivotModeChangedEvent 

onColumnPivotModeChanged = (
    event: ColumnPivotModeChangedEvent<TData>
) => void;

interface ColumnPivotModeChangedEvent<TData = any> {
  // The grid api. 
  api: GridApi<TData>;
  // The column api. 
  columnApi: ColumnApi;
  // Application context as set on `gridOptions.context`. 
  context: any;
  // Event identifier 
  type: string;
}

2. getRowGroupColumns()

function getRowGroupColumns(): Column[];

Example

main.js

const VueExample = {
  template: `
        <div style="height: 100%">
            <div class="example-wrapper">
                <ag-grid-vue
                style="width: 100%; height: 100%;"
                class="ag-theme-alpine"
                :columnDefs="columnDefs"
                @grid-ready="onGridReady"
                @columnPivotModeChanged="columnPivotModeChanged"
                :defaultColDef="defaultColDef"
                :autoGroupColumnDef="autoGroupColumnDef"
                :sideBar="sideBar"
                :rowData="rowData"></ag-grid-vue>
            </div>
        </div>
    `,

  methods: {
    onGridReady(params) {
      this.gridApi = params.api;
      this.gridColumnApi = params.columnApi;

      const updateData = (data) => params.api.setRowData(data);

      fetch('https://www.ag-grid.com/example-assets/olympic-winners.json')
        .then((resp) => resp.json())
        .then((data) => updateData(data));
    },
    columnPivotModeChanged(params: ColumnPivotModeChangedEvent){
      const rowGroupList = params.columnApi.getRowGroupColumns()

      console.log(rowGroupList.map(rowGroup => rowGroup.getColId()))
    }
  },

Reference

Grid-event: columnPivotModeChanged

Column-api: getRowGroupColumns

I hope this helps