Fundamentally, there are two types of "more", with some overlap.
There's the specific person, and the specific topic.
With regard to the specific person, you have to respect that their time is short and you'll have to fit yourself into their existing schedule. The question you will ask is "What courses are you teaching next year?" Unless you are very early in undergraduate studies, You are helping the faculty member by asking this question. Special topics courses get cancelled unless enough students enroll, and if you have the prerequisites, you'll get to hear more of the teaching style that works well for you and simultaneously help the professor keep his course on the schedule.
With regard to the specific topic, it's always appropriate to ask about practical applications to a theory course ("How would I use this?"), practical aspects of an applications course ("Can this fail?"), theory behind an applications course ("Is there a mathematical test to see whether it will be stable?"), what the professor would like to have included in the syllabus if the course were more hours, and whether the course material is applicable to the professor's own research. You may get lucky and be given pointers to notes or recordings prepared by the professor, but most likely you'll be pointed to other resources. Don't discount them when you back back out through the office door, this pays off proportionately to the effort you put in. Likely there will be an opportunity to talk about what you discovered from the resources suggested (assuming you actually put in the time to study them) when you next see the faculty, but even if not, you still learned new things.
Finally, most faculty will take some time to answer general sorts of advising questions about the curriculum of the department and/or professional development and career paths. Their research is always a possible topic for discussion... but unless you ask how it relates to the class and go out and learn more on your own, these are likely to be one-off conversations.