How can I set -X (X11Forwarding) in my ~/.ssh/config file for a specific host?
If you peek into the manual page for ssh_config, you will find an option ForwardX11, which can be put in your config such as:
Host wk
Hostname W.X.Y.Z
ForwardX11 yes
And then your connections to host wk will have X11 forwarding enabled by default.