The general approach to doing something like this would be (and it is difficult in this case).
1. Run your Distribution through Automation
2. Run Capability Analysis
3. Use GetGraphicItemByName or GetGraphicItemByType on the Distribution object to get the TableBox display box that contains CPK. In my case, this was the 5th table box but it can vary depending on the analysis.
4. Use TableBoxMakeDataTable on that table and then read the CPK from that data table <OR>
5. Use NumberColGetItemText to get the numeric value within the table box (you must get the NumColBox first).
As I said, this is a complicated operation. I hope this helps.