Descartes defeats universal skepticism with the cogito. But is the cogito something we can really be certain of? And what is the source of the certainty? For a start on these problems I would consult Jaako Hintikka's article "Cogito Ergo Sum: Inference or Performance?" in Sesonske and Fleming Meta-Meditations, Wadsworth Publishing Co. Belmont Ca. Another interesting discussion of how successful Descartes is in defeating skepticism is found in Richard Popkin's The History of Skepticism, University of California Press. Still another fine book is Curley's Descartes Against the Skeptics, OUP. There are many excellent general studies of Descartes which also include discussion of the problem posed by skepticism.
One reasonably clear cut, though difficult, paper topic is provided by O.K. Bousma's paper "Descartes Evil Genius" in the Sesonske and Fleming volume. Bousma's strategy to defeat skepticism is to show that the skeptical hypotheses which Descarts thinks are perfectly legitimate are in fact incoherent. So, the philosophical problem with which you are confronted is this:
BOUSMA AGAINST DESCARTES
Descartes assumes that his dream hypothesis and the Evil Demon hypothesis which he employs to call more and more of his belief into doubt are coherent skeptical hypotheses. As such he is hard pressed to answer them, and one may doubt how effective the answers are. Bousma claims that Descartes was wrong to assume that these skeptical hypothese are coherent. He gives arguments to show that they are not. The problem is to determine which of these two philosophers is correct and to supply convincing arguments in support of that opinion.
You would need to explain Descartes' skeptical hypotheses and perhaps his solutions to some of them, Bousma's arguments to show that these hypotheses are incoherent, and then add an argument of your own either to defend the Cartesian position that these skeptical hypotheses are legitimate, or give some additional argument to show that Bousma is right.