Adults I don't have a problem with. I want to learn how to sex them as chicks. @Myshire Farm Quail mentioned that they sex their quail at 3 weeks, so I want to learn how to do that too.
That's mostly just through experience. I was able to sex mine at about 5 weeks and I was about 50% right (luckily I had more girls than I thought). One thing to know is that girls will still have a thin layering foam, especially if you accidentally squeeze hard enough, so don't just put every bird with a drop of foam in the male pen.
Also try not to sex during mating since the females will show the foam the male's just got in them
These help me know what I'm looking for.