Hi Jeannie. I have tutored the SAT and other college entrance exams for years, and quite honestly, none of the exams actually require knowledge of particular texts. The reading portion of the SAT simply presents students with short passages and then asks questions on the basis of those passages. The ACT is the same way. The SAT subject test in Literature (which I am assuming that your student will also be taking) also presents short passages or poems and then asks questions on them, although the passages are from works of literature rather than from non-fiction prose. There is, I suppose, a small chance that one of the passages for the Literature test would be a passage from Faulkner, but in any case, all of the questions would be answerable on the basis of the passage alone. (In fact, some students find that having actually read and studied the text makes the questions more difficult since it is harder to separate what the passage actually contains from what the book as a whole contains or from what was discussed in class.)
I'm sure you and your student have already talked about other, more practical ways of preparing for the SAT, which would include a test-prep course. I would highly recommend studying with Kaplan, as I think they have one of the best set of strategies out there. They also have a more healthy and helpful attitude towards the test than some other companies out there.
You might, however, be speaking about preparing your student for the AP test in Literature, which actually does require content knowledge of literature, at least for the essay section. Unfortunately, that is a test which I have never taught, so I'm not terribly qualified to make the best suggestion. Nevertheless, I would think that The Sound and the Fury would likely be your best bet. Alternatively, you might consider Absalom, Absalom or As I Lay Dying.
I hope this was helpful! Good luck to your student!!