When booting, I'd like to see the kernel output without having to edit the GRUB line on each boot. How can I do that?
Open a terminal (Ctrl+Alt+T) and issue the following command
pkexec gedit /etc/default/grub
sudo -H gedit /etc/default/grub
I assume here that gedit is installed on your system, if you prefer another editor use the appropriate name (e.g. leafpad, kate...etc).
Search, find and edit the line
proofread, save the document and then run in terminal