Women tend to be pretty forthcoming about their cumming, especially post-coitus. So the easiest way is just to ask: "Have you learned to orgasm from sex? Or only from your clitoris?" That's assuming she didn't orgasm during Round 1 with you. If she did, then it's just, "Man, that was fun. Those kinds of hard orgasms like that, is that pretty typical for you?"
From there it's an easy segue into a conversation about when she had her first orgasms, how she learned to cum, and so on and so forth.
As for partner counts, you can always just ask -- again, post-coitus is the best time for honest(-ish) answers.
However, you can often sort of tell just by a woman's comportment/behavior.
Check out my article on gauging women's partner counts.
As for the "I've never had an orgasm but I've had sex with 50 men" chicks, typically it is mostly one-night stands, where the sex is drunk and bumbling and the connection is not that intimate. So it makes sense she'd not have had a guy who helped her break through to orgasm. Also typically these girls have some kind of issue -- self-esteem, or childhood abuse -- where they seek comfort from anonymous sex, then run from close relationships.
Because if a woman is only engaging in sex for the pleasure, she will tend to learn to cum pretty quickly. She's having a great time, her defesnes go down, and she starts cumming.
Remember that lots of partners doesn't necessarily mean lots of sex. If she's had 50 men, but all but three have been ONS, and the three that weren't ONS were mere short-term lovers she didn't stick with long, she's had a lot less overall sex than a woman who's slept with only a few guys and had long and sex-filled romantic relationships. She's also missed out on the supportive environment necessary for most women to learn to cum.