I'd say anything that will help *you* decide who gets your vote. I'd hope the things that would help you decide would be relevant to the Party in some way!
It can be about the current role of the Board, potential future ones that you or the candidates might like. The PPUK-related views of Governors impacts the way they do aspects of the job - so absolutely fair game.
You can ask in candidate threads, asking them all the same question, or all different questions, if you have a question to all candidates you might want to start a new thread and then link to it in their threads to make sure they spot it ...
whatever and however you think best (within reason)