How many times one can ask a given professor a question depends on the professor. There are professors who do not like questions ("this is not a good question"). There are professors who will forget about the rest of the class to attend to a question, however, misguided, spending five minutes answering whatever nonsensical question, boring the rest of the class in the process.
The size of the class matters. It can be difficult and even problematic to handle numerous questions in large lecture halls. Once there are more than 80-100 students in the room the dynamic of answering questions changes. The student can be physically far away from the professor. Attending to individual needs does not always help in maintaining the concentration of a large group of people.
Nonetheless, my sentiment, I think shared by many professors, is that most students do not ask enough questions.
Questions can be valuable for the professor because sometimes they signal or highlight particular misunderstandings and confusions, and generally what is asked by one student could/should be asked by many. The professor is gleefully talking about computing the flux of an electric field across some surface and the student asks what that $\Omega$ thing below the integral sign is ...
On the other hand, there are occasional students who really do ask too many questions. Most semesters I don't have one of these students in class, but last semester I did, and it requires some work to handle it well. The potential problem is that the constant questions interrupt the flow of class and distract other students. These problematic students tend to act like class is a private tutoring session, and what characterizes them is the indiscriminate nature of the questions they ask - they ask about notation, about the meaning of the logarithm, about philosophically why we need to parameterize surfaces, about famous French engineers, etc. Usually this is a sign of immaturity, of someone who has not yet learned to censor himself or lives in a mental bubble, blissfully unaware of those around him. Also it can indicate a poorly developed ability to distinguish between the trivial (the professor's handwritten $u$ and $v$ look too similar, but from context it is obvious, upon reflection, which is which) and the meaningful (the problem turns on whether that $u$ is really a $v$). Some very strong students ask a lot of questions too, but these are usually distinguishable from the problematic ones because of the quality of the questions they ask. I don't mean that they ask sophisticated high level questions - I mean that they ask questions that address a basic and key issue, even if elementary.
As a student, how to tell if you are asking too many questions? If you are asking yourself that question, it is highly likely that you are not asking too many questions in class. The self-awareness to pose the question suggests a sense of limits that suggests it is unlikely that who asks it is passing those limits.