For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:markusd:x2go/openSUSE_Tumbleweed/home:markusd:x2go.repo
zypper refresh
zypper install x2goclient
For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:markusd:x2go/16.0/home:markusd:x2go.repo
zypper refresh
zypper install x2goclient
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:markusd:x2go/15.6/home:markusd:x2go.repo
zypper refresh
zypper install x2goclient