I think good general questions would be

What in your opinion are the mods doing right
What in your opinion are the mods doing wrong 
How in your opinion can those things be fixed

And some scenario based questions, based on actual or hypothetical problems the mods have faced before or are likely to face in the future.

What can we do to improve transparency
What can we do to improve the three key aspects of Fairness, Firmness, and Consistency