A remarkable point of this community is that it makes people realize that academia varies more than you think it does.
One of these variations is the structure of the different education levels. While the PhD level has a somehow clearly distinguishable character everywhere, the structural difference between the Bachelor's level, which counts as undergraduate education, and the Master's level, which counts as graduate education, might be more fuzzy.
In many European countries, before the Bologna process, there was not really such a thing as an undergraduate education: you would have studied for 4-5 years straight and got a Master's, without getting any Bachelor's.
After the Bologna process, many things have changed, but in several cases the way in which education is organized at the Bachelor's and Master's levels is exactly the same. Master's courses are just more advanced, and you don't get an advisor until the very end, when, once exams are almost completed, you start working on your Master's thesis.
Thus, from my point of view, most of the undergraduate questions are automatically generalizable to graduate education at the Master's level. If a student asks about something that happens in a course, there's no difference whether this course is at the Bachelor's or at the Master's level.
What kind of undergraduate questions are not really generalizable to graduate education then? How can we draw a universal line?