Do you know if there is an ISO/IEC preference for using either Candidate or Examinee when referring to the test taker? I see it both ways and would like to standardize our documentation. Also, first letter capital Candidate or Examinee?

You use the terms in different contexts. A candidate is someone who has applied for certification. An examinee is someone who is taking a test or is about to take a test. So all examinees are candidates. But not all candidates are examinees (some candidates haven’t scheduled their test and some have completed their test).

Capitalize as you wish – just be consistent. Hope this helps.