Now that I am back working on XenServer I have been looking at the CCA for XenServer Exam.
Below is the overview of the exam.
Here are some test prep materials that I have found. Most are going to be for XenServer 5, but I can't imagine that XenServer 6 is that much different.
http://citrixxperience.com/free/A09Printable.pdf
http://citrixxperience.com/free/A09StudyGuide.pdf