It is interesting that you phrase your inquiry here as "questions to ask that they would like to hear." I suspect you have a small misunderstanding about the nature of college fairs. A college fair is a gathering of college/university recruiters who want to help you discover their institution and help you make a good match between your desires, interests and your college/university. A college fair is meant to tell you all you need to know about them in order for you to select them (they are asking you to select them at this stage).
Later, when you go for your interviews, the institution will be in the information gathering phase: they will want to know all they can about you so they can select or not select you. It is at this phase that you may want to give consideration to asking what "they would like to hear." Although this strategy may or may not be a wise one to incorporate into your interview phase.
At the college fair, you are the interviewer as later the college will be the interviewer. Some things you need to think and ask about are future career and higher degree oriented questions. At this point you may or may not know your field of interest or your aspirations toward master and doctoral degrees. Yet you might assume you do know and ask some questions that will help you along your way. You might ask how many undergraduae classes are taught by professors. You might ask about opportunities for undergraduates to contribute papers to conferences. You might ask about what research is underway at the college/university in fields you may potentially be interested in or are interested in if your decisions about a major are already made (undergrads rarely participate in research at universities though once in a while there may be an opportunity to do so at a college).
You might ask about future employment seeking opportunities provided. Are there corporate and other job recruiters who come to the college/university looking for job candidates? Are there campus sponsored opportunities to apply for employment before graduation (so you step from the campus to the corporation)? What career counseling opportunities are available for students and for alumni? You might also ask about non-major activity opportunities, like: Is there an all-college choir or band? Are their intramural sports for non-athletic majors? Is there an astronomy club for non-majors?
These are some of the things you will want to know from them. These sorts of questions will also, ironically, help you later when they want to know things from you since you can make well informed and well reasoned remarks and inquires about your field(s) of interest, your future prospects and the campus's opportunities.