Hi,
Best Wishes for your exam preparation. There are infact many feedbacks from colleagues on this forums you can find about this topic, however, I can refer you to my experience as well, perhaps this may be of some help:
https://www.scrum.org/Forums/aft/1057
Regarding your question, reading as much as possible is indeed very helpful but not required if you have experience in working in SCRUM teams and you are witnessed to SCRUM events, participated in SCRUM products.
Only mandatory reading: The SCRUM Guide. do download and read multiple times at low pace , underlining each word and understanding the same. Try to rephase your own understanding on each section if you like.
Best Regards,
Hemant