What's the best way to deal with questions that I don't understand because of accent during/after a talk?
What I usually do is to try to piece together as much of the question as I can and then rephrase/guess/fill in the blank in my own words ("So you are asking whether..."). If my guess is close enough the person asking usually relents. If not, repeat this process until the question is clarified.

In the long term the only solution is to try to expose yourself more often to different accents so that you learn to understand how they differ from the "standard" ones.