Can I play online with an Xbox 360 emulator and register my account via it, or is this only possible offline?
How far online?
Do you want to be able to go to a website and start playing for free right away?
No. Unfortunately this is not possible.
However, I could imagine that there are paid services where you "stream" an xBox. So they have an emulator and you then stream the screen. But I don't know of any such provider. There may be some.
I also found https://www.t-online.de/...phone.html. It's not an emulator, but you can achieve something similar.
If there were hourly Cloud Gaming that would be nice
Would like to play Black ops 2 again
Online I mean that I can log into my account with the emulator and then play my games
You completely misunderstood the question.
It's illegal anyway
Why illegal, I bought the games
Can you play online for free?
Yes, then you have to play it on Xbox 360 360 an emulator for X Box is unfortunately illegal
What a shame