I have access to a CPanel installation. I can also SSH to that same machine. I don't offhand know if SSH is built in as part of a standard CPanel install, or if that was separately done to the server I use.
If the user has SSH access, I would consider this to be very similar to running software on one's own machine. Therefore, on-topic, as SuperUser covers running software.
If the user doesn't, then this really boils down to using a web interface, and I believe that the topic of "how to use a website" may be less on-topic, namely because you may not have "full access" (e.g., you may not be able to remove the software, and install an upgraded version of the software if that fixed things), so this would be more about a service that someone else is providing, rather than software that you are directly overseeing.