The answer to this depends entirely on exactly what you're talking about here.
If you're wondering whether a gynecologist can tell if a woman has ever had an orgasm, then the answer is no. Orgasm does not permanently change the state of the genitals in any way. There would be nothing special for the health care provider to be looking for that would appear different in someone who has orgasmed and someone who hasn't.
If you're wondering whether a gynecologist can tell if a woman has had an orgasm recently, the answer is still likely no. If one has had penetrative sexual activity recently, there can be some signs of that (especially if it was a forcible act) that could be detected during an exam. This is part of why doctors usually ask that you refrain from penetrative sex, tampon use, or douching (which should always be avoided really) for around 48 hours prior to a pap smear or pelvic exam. The presence of semen in the vagina can make it difficult for the doctor to accurately assess the patient. Also, sometimes sex can irritate the cervix or cause little abrasions. With just orgasm alone though, unless we're talking about a case where the woman has been active very recently and still shows signs of arousal, the doctor is still not going to be able to tell about whether or not an orgasm has occurred. Genital arousal takes a bit of time to subside (whether an orgasm occurred or not), so if an exam was done before that had happened, the doctor might be able to tell that she'd been aroused...but nothing beyond that.
If you're wondering whether a gynecologist can tell if a woman has an orgasm during an exam, then the answer is possibly. During arousal and orgasm there are some physical changes that can occur to the genitals. So if the health care provider in question were examining a woman during an orgasm, they might notice the involuntary vaginal muscle contractions that occur, etc. (To be clear as well, this would be a pretty unusual occurrence. A gynecological exam is not really a sexual situation.)
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