I'm a TA who is assigned to help grade papers for an upper level course. In the first assignment, I realized that I do not know how to do one of the assigned problems. The professor has requested that I grade all of the assigned problems. I don't think I will get a grading rubric (showing the answers to the assigned problems). I'm extremely nervous since I don't know how to do all of the problems on my own.
Should I ask professor directly about the problem in his office hours? The alternative would be to look at all of the solutions submitted by the students and analyze which answers are correct.