My experience with these interviews is that mostly they will tell you things. For example, I have always gotten a long disquisition on tenure without making any prompts, as well as general discussion about the university. It is possible they'll ask for your thoughts on general topics in education or research (for math, I think the connection between pure and applied math is popular). Grant funding isn't an issue that's come up for me; I don't think it's what people usually have in mind for math but it certainly wouldn't be a surprising topic. Certainly it would be smart to have a few general questions (where they see the university as a whole going, how your department will fit into it) at the ready, just to fill any dead space. I suspect the main thing is to just come across as a normal person. While deans sometimes try to influence hiring based on general considerations (the direction of the department, diversity, etc.) I've never heard of them trying to use their impressions from the interview for this (with the exception of Leon Botstein).
Also, don't hesitate to ask people in the department what it would wise to discuss with the administrators. They'll know better than us yahoos on the internet what their deans' bugaboos are.