Starting GUI program over SSH in wayland (Ubuntu 17.10)
X11 is way old tech at this point. To do this with wayland, check in a GNOME Terminal window:
$ echo $DISPLAY $XAUTHORITY
:0 /run/user/1000/gdm/Xauthority
In the ssh session, define those two values:
XAUTHORITY=/run/user/1000/gdm/Xauthority DISPLAY=:0 gedit
Verified to work on Ubuntu 19.04.