Is this report to show individual hands, or your stats split by position?
I assume it's individual hands as you can see stats by position on the Positions tab.
If you want to see the position for individual hands you will need a custom stat - in the Holdem Cash Hands section there is already a column called "position", so you just need to make a stat to display it. Create a new stat with a Value Expression of just "position", fill in the Format tab, save it and add the new stat to your report.
See the
Tutorial: Custom Reports and Statistics for information on creating custom stats.