Add repo
vi /etc/apt/sources.list.d/x2go.list
Add
deb http://packages.x2go.org/debian stretch extras main deb-src http://packages.x2go.org/debian stretch extras main
Add key
apt-key adv --recv-keys --keyserver keys.gnupg.net E1F958385BFE2B6E
Install X2Go server with
apt-get update apt-get install x2goserver x2goserver-xsession -y
Now you need to install one of the Desktop, it is better use XFCE on remote servers.
apt -y install xfce4