X11 forwarding should be first enabled both at the server and client ends.
At the server end, put "X11Forwarding yes" in /etc/ssh/sshd_config, restart SSH daemon and it should be able to forward X11 requests.
At the client end, connect with "ssh -X
Host *The last line is not needed if "ssh -X" works. In some circumstances only "ssh -Y" does, then ForwardX11Trusted is necessary.
ps1. If network is slow, "-C" (compress) may help.
ps2. X must be running with "-nolisten" argument, which (I guess) is the default in most distributions.