Great question.  You actually have a lot of flexibility for a Contract Discrepancy Report (CDR) as there is no mandated format or content checklist to follow.  Unless of course your local organization or contracting officer has a preferred method/format.

That said these are the common elements most CDRs have:

Administrative Information: contract number, dates, corresponding contract information impacted (CLINs, PWS or SOW parargraphs, specifications, drawings, etc. impacted)

Facts: what is the non-conformance, what part of the contractor’s effort is not meeting contractual requirements?  Date(s) of occurrence, inspection results, etc.

Contractor’s Response: root cause analysis (if any), rationale, etc.

Government Actions or Response:  recommendations or formal technical direction given to the contractor, proposed remedies, etc.

Here are a few resources to help you:

a) The DD Form 2772:  This is a non-mandatory DD Form which can be used to document a contractor discrepancy.

b) WIFCON post:  This is a link to a WIFCON post showing an example of a structured surveillance approach and documentation of a CDR.

c) Guidebook for the Acquisition of Services: see section 7.3 page 55.

d) Finally: FAR part 46 and DFARS part 246 (and your agency supplement) has additional information related to inspection and acceptance and non-conformances.