For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:psych0naut:x2go/openSUSE_Tumbleweed/home:psych0naut:x2go.repo
zypper refresh
zypper install x2goclient
For home psych0naut branches openSUSE Factory openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:psych0naut:x2go/home_psych0naut_branches_openSUSE_Factory_openSUSE_Factory/home:psych0naut:x2go.repo
zypper refresh
zypper install x2goclient
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:psych0naut:x2go/15.4/home:psych0naut:x2go.repo
zypper refresh
zypper install x2goclient
For 15.3 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:psych0naut:x2go/15.3/home:psych0naut:x2go.repo
zypper refresh
zypper install x2goclient