I used the following resources that were extremely helpful in preparing for the CDIP exam:
Clinical Documentation Improvement Principles and Practice AHIMA Press
Clinical Documentation Improvement Achieving Excellence AHIMA Press
AHIMA practice briefs, CDI Toolkit and Coding Guidelines
AHIMA also has the CDIP practice exam, and prep series that would also be very helpful for preparing for this exam.
I also used the CCDS study guide found on HCPRO/ACDIS and Optum's CDI reference guide as additional resources.Thanks,