What is a good title for a critical paper for "Sir Gawain and the Green Knight?"
Based upon the story of Sir Gawain and the Green Knight, I would probably look to the poem for an idea that could inspire a title for a critical paper. Because Bertilak is testing Gawain's integrity and honor, and perhaps based on the fact that Gawain is totally honorable except for the magic belt, maybe a title reflecting adherence to one's code of honor might provide you with some direction.
I have listed a number of possible titles. The final decision will probably fall with your own response to the story. A critical paper would still require you to take a stand as to whether Gawain is a disgrace to Arthur's court, or whether he can be forgiven his small fault in wishing to remain alive: even the Green Knight, Bertilak, understands this in Gawain.
Gawain's Faltering Honor.
Sir Gawain: Failed But For Love of Life
Sir Gawain's Worth
Gawain's Enemy Finds Him Worthy
Bertilak's Compassion in the Face of Gawain's Fault
I hope one of these helps you find a title that suits your sense of Gawain and his internal battle to be an honorable man.