If you need to provide debugging of your CoreData apps, you can track what is happening statement by statement by modifying the Scheme.
In XCode, click on Product in the menu, and then Scheme and then Edit Scheme (or just Cmd <.
For the Debug Run mode, choose the Arguments tab and add to the Arguments passed at launch.
Add -com.apple.CoreData.SQLDebug 3 and hit OK. The value 3 should provide enough information but higher numbers provide more verbosity.