To followup a little on Benny's response....
If your purpose in reading the book is to pass the test, then you can probably formulate questions that you'll be asked, or are likely to be asked, based on a) previous exams from this professor, and b) this book.
You might want to characterise the questions you've had from this teacher before.
Some general questions, which can't hurt:
Who are the characters? What are the important scenes? Are there any wacky plot twists? Is there a passage that "rings true"? What is the most intense scene in this book? What is the most memorable? Is there some great dialog?
There might also be meta-questions (depending on what level you're at), such as, "why is this book important?"
Finally, I've found that reading a book the "old fashioned way" once I've photoread makes the reading go much faster, and easier to remember.
Good luck!