Currently the best study materials are the notes from your 100 hour basic course if taught by a certified teaching diplomate.
The links listed below are the reference materials for all questions on the Diplomate exam
AK Flow Chart Manual - David Leaf
AK Flow Chart Manual Digital - David Leaf
Applied Kinesiology Synopsis 2nd Edition - David Walther
Applied Kinesiology Synopsis 2nd Edition - KOREAN Version
Applied Kinesiology Synopsis can also be purchased from Amazon
Applied Kinesiology Workshop Manual 2000-2007 - Goerge Goodheart
Common Glandular Dysfunctions - Walter Schmitt
Compiled Notes on Clinical Nutrition Products - Walter Schmitt - CURRENTLY OUT OF PRINT 2016 WAITING FOR UPDATE ON NEW VERSION
Applied Kinesiology: The Missing Link in Health Care - Scott Cuthbert
Applied Kinesiology: Clinical Techniques for Lower Body Dysfunction - Scott Cuthbert
Textbooks and study materials for the German version of the Diplomate Exam
Textbooks and study materials for the Russian version of the Diplomate Exam
Some questions on the exam come for two sources that are no longer available to purchase, and the board is currently trying to rectify this situation:
George Goodheart Research Tapes - Currently unavailable to purchase 2016
George Goodheart Yearly Research Notes - Currently unavailable to purchase 2016