LeandingAnswers has a posting on sample ACP questions for those thinking of taking the exam. I don't have an independent assessment of how accurate these questions are, but they seem reasonable for the purpose.
The sample questions cover the landscape, from the Agile Manifesto and Principles, through burn charts and teams, to velocity calculations and SCRUM ideas.
To answer accurately, you should know stuff like Principle #2, honoring change, is about the time period: early in development vs late in development.
And, would you know where the business investment in the backlog is best applied? If not, you should review how agile involves the business in the requirements business. After all, business holds the proxy for stakeholder interests in the project, and really no one else does.
Some questions are framed such that the idea is to look for something to eliminate. Sometimes, it's a matter of eliminating the worst of the possibilities, even though all may be possible.
Of course, LeadingAnswers is not an exclusive place to look for help on the ACP. A Google search turns up all kinds of help... as you would expect with something with this much interest (and need I say money?) behind it?
For those of you who read this blog regularly, you know I am one of PMI's instructors for their eSeminarWorld course on Agile Project Management. So, now you know (disclosure)