Download the .repo file and save it to the correct location:

wget -O /etc/yum.repos.d/x2go.repo http://download.opensuse.org/repositories/X11:/RemoteDesktop:/x2go/RHEL_6/X11:RemoteDesktop:x2go.repo

Hint: If you are behind a proxy, make sure the proxy is defined in /etc/yum.conf. Standard yum repos do not use the same connection mechanisms as rhn channels.

Congratulations, you are now able to access the X2Go packages. You may continue by installing x2goserver, x2goclient or pyhoca-gui or any other of the available packages.

Installation instructions for X2Go Server