The IBC itself is all you need. A handbook or commentary is also helpful.
My suggestion is to study in this fashion:
First, learn how the code is formatted and arranged. Next, learn what the title and scope each chapter is. Next, break down each chapter into th specific articles. Finally, learn the individual sections of each article.
Read and re-read the definitions as often as possible. Terminology is everything when taking exams and in the real world.
Study hard, be dedicated to your studies, and over-prepare.