I've been through one...mainly asked questions like:
-"With additional hours, do you think the DEV could be successful? Why/why not?"
-"Anything you think you could have done differently as a OJTI?"
-"Did DEV ever acknowledge they were struggling?"
-"Did you see the DEV studying?"
-"What areas is the DEV struggling with?"(I.e.,Understanding rules and/or applying the rules)
-Reviewed training plan/reports...made sure all the Is were dotted/Ts crossed
Had NATCA, local management, & an outside the facility chair in the room asking the questions.