Following snippet code will show the total grouped columns on OnAfterResponseProcess event in javascript.

<script>
    function ShowGroupedColumnsCount2(controlId, actionName,
        lastRequestObject, xmlResponseObject)
    {
        var grid = ISGetObject(controlId);
        var rootTbl = grid.RootTable;
        var grpColumns = rootTbl.GroupedColumns;

        alert(grpColumns.length);
    }
</script>

<ISWebGrid:WebGrid ID="WebGrid1" runat="server" ...>
    <LayoutSettings AllowGrouping="Yes" GroupByBoxVisible="true">
        <ClientSideEvents OnAfterResponseProcess="ShowGroupedColumnsCount2" />
    </LayoutSettings>
    ...
</ISWebGrid:WebGrid>

The collection of grouped-columns can be accessed in [WebGrid id].RootTable.GroupedColumns. This should helps.

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