Comment # 9 on bug 969098 from Takashi Iwai

(In reply to Daniel Bauer from comment #8)
> I really feel stupid... but I can't find where to add this boot option.
> I pressed "e" on the highlighted menu entry and get a screen "setparams
> 'opensuse leap 42.1". I entered
> plymouth.enable=0
> at several positions, at the very beginning, in the middle... then pressed
> F10, and get the black screen...
> 
> it seems this is not the way to do it :-)
> 
> How and where do I enter this option?
> 
> sorry again for being so ignorant...

There should be a line like
  linux /boot/vmlinuz-4.4.3-.....
or
  linuxefi /boot/vmlinuz-4.4.4-.... 

In either way, it should contain words like "splash=silent quiet showopts".
Append your own option to this line, then press Ctrl-X to continue to boot.

HTH.