Are you trying to verify before an independent audit, or just as an in-company initiative to gain an understanding of where things are currently?
At any rate, compliance is best examined in just the way you think it would be (at a very basic level) - you have certain requirements that are expected to be met, and you need to examine existing process and artifiacts to confirm that not only are particular processes in place, but that they're actually followed on a regular basis.
The SEI operates an Appraisal program called SCAMPI (Standard CMMI Appraisal Method for Process Improvement). This can only be officially carried out (if you want the results to be public) by a certified lead appraiser. As has been stated this is money, you could attend the courses but in general these are targeted at third party companies that will be doing external appraisals.