Advice on a Gap Analysis

For the first assessment, does the gap analysis have to be performed against practices or against work products?

There are no specified standard requirements for a Gap Analysis. The Gap Analysis is intended to identify major differences between a model standard and actual practice. A Gap Analysis may involve just reviewing documents, just interviewing people, or a combination of both. I like to evaluate a combination of documents and people for a Gap Analysis. This approach yields the best results, because in many cases the process as practiced is different from the process as documented.