What unanswered question do you have about this story?
The previous poster's thoughts are exactly right. In the end, no one can really develop a set of questions for you. The experience of reading this story about individual perception of reality is simply that- individual. The questions will differ from reader to reader. I think that I can give you some starting points that can possibly start this process in your own mind. I think a good question could simply be if you felt the ending was a satisfying one? Given how the story developed, did you feel it ended in an appropriate manner? Another one might be centered on the idea of the nature of the relationship between husband and wife, and whether or not you think such dynamics are present today in domestic relationships.
I don't really have any unanswered questions about "The Yellow Wallpaper," and if I did I couldn't really answer this question for you. My questions would probably not match yours. All you need to do is read the story and see what unanswered questions you have when you've finished.
My guess is that you might have questions about what the woman is suffering from, what exactly she sees in the patterns in the wallpaper, what is the meaning of her circling the room at the close of the story, and what does the future hold for her.
You also might wonder if her husband is okay. But, again, simply read the story and see what questions you have.