And just to add on the excellent suggestion from jrw159... If you go to your section meeting for your region and contact the person responsible for the library, or the section, or certification chairperson, you could purchase the AWS code books as well as other reference books also... By going that route, you can purchase the study material at a substantial discount, and your section representatives will also steer you in the right direction with which books to purchase, so that every topic covered in the CWI/CWE body of knowledge will be taken into account for you to study further as well as suggestions that will be helpful in preparing yourself for the exam...
Also, most sections do hold meetings, and workshops that specifically cover preparation for the CWI exam which is something to consider as well since they are very good in giving you a better perspective of what you need to prepare yourself for prior to taking the exam, and take as much time to prepare yourself before you take the exam...
I mean, take at least a minimum of six months to a year if necessary to study because if you don't, you will be overwhelmed and almost certainly fail the first time especially if you are not aware of all of the topics covered in the body of knowledge, or have given yourself enough time to study the code your are going to take for the open book portion of the exam, or have given yourself enough practice time with measuring discontinuities, or defects by using the various visual inspection tools as well as reviewing high school math and studying the part B practical exam portion of the exam also...
So, take your time and seek guidance from your local AWS section folks, and ask them for help, and do not take the exam unless you sure that you are really ready for it by finding out as much as you can what you need to prepare yourself for it and giving yourself enough time to prepare for it!!! :) :) :)
Finally, Don't be afraid to ask as many questions you can come up with because, the folks at your local section as well as the many excellent folks in here will give you some good suggestions and if you use the search function in the forum, you can find many, many threads covering a multitude of queries regarding the CWI exam and how to prepare one self for achieving the best possible outcome which of course is to PASS!!! :) :) :)
Respectfully,
Henry