The Organisation Case Notes permission lets you add, edit, and view case notes for an organisation.
Two other permissions can also give you the ability to view organisation case notes, even if you don't hold the Organisation Case Notes permission itself:
Delete Case Note permission.
System Amend Case Note permission.
This is because the system assumes that if you're trusted to delete a case note, or to amend one that's already been finished, you must also be able to see it first. Both permissions carry viewing rights alongside their main function.
You don't need the Organisation Case Notes permission specifically to view organisation case notes. Holding either of the permissions above is enough on its own, and this is expected system behaviour.