Well preparing for any exam is always dependant on previous experience with the
testing topics. Have you been an SQL Query builder for a while or just starting. Have you been working with Oracle for a bit? Those are the questions that kind of determine how long it takes to prepare.
I haven't found any free mocks, so if anyone else has links, let us know.
Have you taken Oracle's class on Intro to SQL? Everything that is on the test is from that class, and book.
Mark