Let's jump right in to the deep end. Every once in a while I see the question posed somewhere: Can a woman be trained to orgasm on command? They aren't even asking how it's done; they're just wondering if it's possible. Well ... not only is it possible, I think it's often pretty easy, at least within a dom/sub relationship.
In fact, a trance-induced orgasm is what led us quickly into this whole realm.
Let me tell you what I did, and then I'll extrapolate wildly and suggest how other doms might accomplish the same thing.
I hypnotized e for the first time about two months ago. We were chatting online, voice to voice; she said she'd never been hypnotized before; but I talked her right into a trance without much trouble at all.
I didn't make her cum right away; I stalled maybe five minutes while I first made her feel light, and then warm. Then I just told her to cum. Over the headset I heard her squeal and moan pretty violently. A couple of minutes later, I woke her up. She remembered nothing of her climax. Frankly, I don't think she believed me.
So the next time she was in a trance, I planted a little trigger, a command for her to obey after she woke up. She woke up; I spoke the command; she came. Now she was impressed.
These orgasms are now a completely routine part of her day. She cums at least eight times a day (immediately after peeing), and usually several more as a result of direct commands during our conversations. (Example: Just a few minutes ago, in a crowded living room, she came for 15 seconds, with only the hypnotically induced tape across her mouth keeping her from singing out.) Sometimes she has objects, real or imagined, inserted at the time; sometimes she's frozen like a statue when it happens.
This isn't the first time I've done something like this. A few years ago, I trained a sub to put an orgasm "trigger" in a fairly innocuous part of her anatomy -- that hollow at the base of the neck. If either she or I touched her there, she climaxed without hesitation. Now, I don't remember all the steps I took to get this effect, but a key one was to stroke her there, over and over, and tell her to feel it in her clit. In retrospect, I think she was in a near-trance much of the time we were playing.
Further evidence that orgasm on command is possible: The various fetish videos floating around. One hypnotist favors the word "kapow" as the trigger for his subjects' orgasms. They look quite real to me.
As remarkable as this all sounds, I suspect it happens like this:
Most dom/sub partners have played orgasm denial/permission games. The hotter she gets, the more she begs for release, the stricter you get; the desperation builds; finally you relent and say "cum" or "now" or "go, slut" -- and within seconds she's oscillating. Play that often enough, and intensely enough, and her mind and body learn to associate your command with the physical changes needed to trigger orgasm.
If you are then able to put her into a trance -- and I think most subs will readily go there -- then you can instruct her subconscious to isolate that well-learned trigger. When you say "cum," she will simply cum, skipping entirely over the preliminaries.
But as much fun as it is to watch a woman in a trance having an orgasm, it's a lot more fun if she's awake to appreciate it. So I would go to the trouble of learning how to plant a post-hypnotic suggestion, a trigger, that you can pull as often as you like, after she's awake again.