You would affix a pressure gauge and some adapter fittings for the pressure and/or return to perform pressure test(s) and volume testing (gpm). The fittings are metric, so that would mean some -AN, fittings from a hot rod shop etc. ?
If you suspect problems, a reman power steering pump with reservoir is so inexpensive, why bother with further diagnostics? If you are concerned about the reman quality, keep your core and pay the core price. .
Good luck
Andy