If you want to get the actual record, you can use code like this.
private void gridGroupingControl1_TableControlCellDrawn(object sender, GridTableControlDrawCellEventArgs e)
{
GridTableCellStyleInfo style = e.Inner.Style as GridTableCellStyleInfo;
GridRecord record = style.TableCellIdentity.DisplayElement.GetRecord() as GridRecord;
if(record != null)
{
Console.WriteLine(record);
}
}
If you really want the index, then you can get the record as above, and then call grid.Table.Records.IndexOf(record) to get the index.