1. See an egg layed = girl
2. See it crow = boy
3. See it mate = one on top is a boy, one bottom is a girl
4. vent sex, squeeze its bum hole. Needs to be sexually active about 6-7 weeks at the earliest I think. If you see foam = boy. No foam = girl
Two people have answered your question. You can't feather sex tuxedo quails. You just can't.
Number 3? Yes one on top is a boy, but the one on the bottom is not always a girl! Gay quail sex exists.