I can’t find a command for selecting the next event (midi-note) in the key-editor. I supposed that the arrow keys should work but they don’t.
Any Help?
Normally, this does work (and I can’t think of anything that would prevent it from doing so).
Was this just a “freak occurrence”, or does it never work? (If the latter, try the “sledgehammer” approach, of trashing Cubase Preferences).
Also, before grabbing the sledgehammer, 
hit the right or left arrow key, then immediately open the key commands dialog. The last command used should be highlighted.
Have tried to hit the left arrow key and then immediately go to key commands. No luck. 
If you are saying that nothing was selected in the KC dialog, then you have possibly removed the command, or as Vic said, your prefs are corrupt.
For the former go to the Navigate section in the KC dialog and check if “Right” and “Left” have keyw assigned to them.
Okay! they were gone. But I couldn’t find the right word for this: next event- I didn’t think of “right” 
Thanks!