If it's a "proficiency check" then it will be being conducted by a flight examiner. If successful it will be PICUS, if not then PU/T.
As PP said, who logs what on a "check out" depends on the exact circumstances of the flight, which can vary considerably.
Wolves flyer, if you can be a bit more specific, you'll get a better answer. What are the licence, rating, medical, currency of the people involved? Is it a club or group aircraft? Why is it being done?