Here is some code you can use in the ButtonClicked event.
private void gridGroupingControl1_TableControlPushButtonClick(object sender, GridTableControlCellPushButtonClickEventArgs e)
{
int row = e.Inner.RowIndex;
int col = e.Inner.ColIndex;
GridTableCellStyleInfo style = e.TableControl.Model[row, col];
//get some record data
GridRecordRow grr = style.TableCellIdentity.Table.DisplayElements[row] as GridRecordRow;
DataRowView drv = grr.GetData() as DataRowView;
Console.WriteLine(drv[0].ToString() + " " + drv[1].ToString() );
}