freedesktop - Jun 2024 - How to research about DBus to trigger Suspend mode?

Hello,

the question is less about how to trigger Suspend mode via DBus. It is 
more about how to answer such questions myself.

I often stumble across DBus. I find a lot of examples and all this fancy 
"org.freedesktop"-like strings for methods/objects/services related to
DBus.

But how do I know which one to use? Is there a catalog somewhere? Is 
there a logical system behind it I have not understood yet?
And how can I be sure that the used name-string is persistent on all GNU 
Linux distros and their desktop environments?

Thanks,
Christian