I’m not sure where Yuvan got those instructions from but registercloudguest (as the name suggests) isn’t a general command available on all instances of SUSE Linux Enterprise.
The -r option to zypper expects a .repo file which is not part of the suggested URL.
However if the server is not registered then I would not expect it to be able to access SUSE’s update repositories.
Is the SUSEConnect utility really missing? What does rpm -qa suseconnect* report?
If it doesn’t output anything I’d suggest grabbing the latest version of the suseconnect-ng package from https://scc.suse.com/patches/ - search for suseconnect in Product “Basesystem Module”, Version “15 SP5”, Arch as appropriate - and installing that.
NO, do NOT use an openSUSE version of a package on SUSE Linux Enterprise.
If the rpm -qa suseconnect* command didn’t report anything then it means a suseconnect* package is not installed.
Do you have access to the media or an ISO (the Full version) of SLES15 SP5 matching the architecture you have? If so, you should be able to mount that to/on your machine and rpm -Uvh the required package(s) as you’ll likely need more than just suseconnect-ng.