No interesting research topics available - should I quit and pay back my stipend?
Please keep in mind that to quit I would have to pay back the semester’s fees and probably any stipend I have received during the semester which could add up to 35,000 USD...


"Probably" the stipend? The "probably" makes me nervous -- I think you should start by quantifying exactly how much you would be on the hook for. It could be more than that, or maybe you misunderstand and this would be zero.


  what would you do if you were in my place?


Impossible to answer, partially because I do not know what your "Plan B" is. You need to develop two detailed plans -- one for staying and one for leaving. Only then can you make a good decision.

I would also consider whether you have any professors you trust to discuss this with -- they may be able to help you find a third option.


  I would like to...know if quitting could possibly affect my job prospects and opportunities


Of course not having a degree is worse than having a degree. Paying 35K USD and still not having a degree seems awful. Starting something and not being successful also doesn't look great. But again, the question is: what is the alternative? If you can transfer to a better program, or get an awesome job, then perhaps it is worth it. For sure you don't want to acquire more debt and then not finish.