For openSUSE Factory run the following as root:
zypper addrepo https://download.opensuse.org/repositories/benchmark/openSUSE_Factory/benchmark.repo
zypper refresh
zypper install piglit
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/benchmark/15.6/benchmark.repo
zypper refresh
zypper install piglit
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/benchmark/15.5/benchmark.repo
zypper refresh
zypper install piglit