“Professor of what?” Is this natural sounding?

“Professor of what” is natural, but it probably has a slightly to very negative connotation, based on your tone. I would probably ask “What is the Professor’s area of study” or “What are they a professor of?”, as more neutral or positive tones.

If you're asking a follow up question "Professor of what course?" sounds more natural. If you're instigating the question, something like "What are you a professor of?" or "What course are you a professor for?" would sound better.

If you are a professor, you’d say “I’m a professor of {insert course here}.” If you’re talking to a professor, you could say “a professor of what course?” but I think the more natural thing to ask would be “what do you teach?” Hope that helps!

What do they teach? "What course?" implies that they teach only one course. A professor teaches a subject or a list of courses. So you need to ask a more general question.

There are definitely more formal ways to say it, but in most cases (since I’m not usually spending time in formal environments), I would just say “professor of what?,” if it comes to questioning the subject. If I want to ask the name of the professor, I would probably say “which/what professor (is it),” referring to the individual, especially if the subject taught is implied or stated. (This can be ambiguous at times, so you can also ask “what’s the professor’s name” if needed.) So to answer your question, yes. It is perfectly natural.

Professor of what sounds good. A lot of comments here are saying “of what course” but that doesn’t sound right to me at all. Yes a course at a university has a professor, but professors teach multiple courses for a given major or field of study. I wouldn’t say “I’m a professor of Differential Mathematics/Object Oriented Programming/Brass Ensemble” I would say “I’m a professor of Math/Computer Science/Music” I would consider saying “Professor of what field?” But I would say “course”

I think I need a little bit more context, but my assumption is that the person you're talking to said something like 'my professor told us [a story]', in which case I would rather just ask "which professor?" And my friend would respond with either the professor's name (if they think I know who the professor is) or something like "my math professor". Your options are definitely natural sounding, just adding how I *personally* would say this

"Professor of what?" Is fine if you're asking what subject they teach. It's a little informal though, I wouldn't say this if you're their student, that would probably come off slightly rude. If you're a friend of a professor, this is fine. If you are a student though, "What subjects do you teach?" For their general field of study or "What classes are you teaching?" For specific courses

"Which courses do they teach?" definitely sounds the most natural. Note that "Professor of what?" without mentioning courses would generally imply you're asking about the focus of their post graduate degree(s), not their teaching schedule. As in, the answer would be, "Oh, they're a Professor of Applied Mathematics." not "They teach Calculus 315."

"What's your field?" That's a fairly succinct question that allows someone to answer in as much or as little detail as they want.

"Professor of what?" Is perfectly normal ***IF*** you say it the "what?" In a rising tone. This indicates you heard"professor of" but did not hear the name of the subject. Otherwise if you were to say "what?" in a flat or imperative tone it would it convey the message that you do not belive that the person is a professor and are trying to pick a fight with the speaker.

In the UK Professor is a role you are appointed to and a title you have as a result, rather than just being a teacher. Even at a university, most lecturers can't call themselves Professor Smith. You need to be appointed to the position.. So here you would ask *what are you a professor of?*

Just FYI, "course" means something different in the UK vs the US (not sure about other areas ...). In the UK, a "course" is what you might call a "degree program" in the US. In the US, it's a specific class, which I think they call "modules" in the UK.

I would understand “Professor of what?” to mean which field, department or subject, not which course. “Professor of what course” works better, but I’d probably ask, “What courses are you teaching?” (Rather than “do you teach,” since they change frequently.)

For me, I would probably say “Professor for which course?” Or “what course does your professor teach?”

To clarify a bit here, you're touching on a difference in British and American English. TL;DR in American English, "course" refers to a specific class that one would take during one semester of their studies with a typical course load being 4 or 5 per semester. In British English, a "course" is the concentration of study for one's degree. If you ask a UK professor "what course?" they will likely say something like "I'm a Professor of Chemistry" while the same question to a US professor will get an answer like "I'm teaching Chem 101 and 201 in the fall semester, but in the spring I have 202 and 302). If your question is directed to a US professor, you'd probably ask "Professor of what?" Or "What department?"