The IIA Standards require internal auditors to assess the effectiveness of their organization's governance processes. It's an understatement to say this is a challenge.
One place to start is with the board of directors (or equivalent). How effective are they in performing their duties?
A leading practice is for boards to perform self-assessments — of the operation of the board, each of its committees, and of individual directors. Perhaps a good place for the auditor to start is by evaluating and providing feedback to the board on the adequacy of board self-assessment processes.
An excellent source for many governance-related topics is the Canadian Institute of Chartered Accountants. In 2005, they released "20 Questions Directors Should Ask About Governance Assessments."
I suggest reading this and considering whether this represents a valid standard against which you can assess the effectiveness of the board self-assessment process.
Here is another resource for your consideration:
If you have good guides for board self-assessment, please share — for mutual benefit.