Hi, this is Bruce Richards, I'm on the CCI board and helped develop the testing program. There really isn't one thing you can study to prepare for the written test. The goal of that test is to determine how broad a candidates knowledge is, so a wide variety of topics are covered. We don't consider the questions to be difficult for experienced fly caster/angler/instructors. You will need to know some basic things about casting, instructing, gear, etc. Usually candidates who are well prepared for the performance part of the test have no trouble with the written, and the reverse is also true. I wish I could be more specific, but the only way I could really be more helpful would be to give you the questions, which sort of defeats the purpose of the test! Any of us would be happy to answer any specific questions you might have about any part of the testing process, except for asking what the questions are, of course.....
Bruce