follow up to the Light = knowledge, can other classes know things: would "guide" be a sort of supplement verb to "know" for Seers and Mages, because that's really what sets them apart from everyone else?

Each Class has supplementary, related verbs, really, so you could say that’s the case. Much like how Maids and Sylphs also Improve and Heal, or how Knights and Pages are known to Weaponize. So yeah, Knowing, Understanding, Guiding…