Hello there! :-D
When I use the PermissionsManager plugin and check the DeathNotes, I see this "cansee" flag that can be toggled but... I really can't figure out what's the use of it. Can someone please explain it to me? Thanks in advance!

Death Notes provides the deathnotes.cansee permission, as listed on the plugin page. Only players who have that permission can see the Death Notes, provided this option is enabled in the config file.
I assume this is what Permission Manager is using.

Ok, so just to make it clear to me, all the players or the group that have it flagged allowed can see the Death Notes messages, right?

Sorry, I missed your follow-up question. Yes, if the config option for is enabled, that is the case.

Awesome! Thanks! :-)