If I install gnome will be used Wayland or Xorg default?
And what other desktop environments are used Wayland by default?
GNOME defaults to Wayland.
None that I know of 
Plasma will default to Wayland in its next release.
As far as full DEs go, gnome is the only one that uses Wayland by default.
KDE/plasma can use Wayland by installing a couple of packages.
There are Window Managers like sway in the community editions that uses Wayland.
I’m using an Ubuntu desktop with gnome. I was using Wayland, but had to swap back to xorg to allow external monitor DPMS standby. If you have a better experience with arch I’d be interested to know.