How does Ixalan drafting work with its double faced cards?
This FAQ has all the answers. Tl;dr: For the majority of tournaments, you reveal all double-faced cards as they are opened. And, since picks are put in a pile in front of you, any opponent can see when you pick a double-faced card. For further details (including e.g. what happens if you don't want to pick a card until you know if your opponent is choosing a double-faced card or not), see the FAQ.

There is also a way to draft completely normally using double-faced cards: tournament officials can open the packs beforehand and sleeve everything in opaque sleeves. However, while Wizards of the Coast does do this at some high-level tournaments, they suggest that your friendly local game store does not use this method so that the store and the judges can't get accused of stealing valuable cards from the packs they'd pre-open.