If a target successfully saves against a charm type spell do they become aware that someone has attempted to ensorcel them? Specifically, I'm asking about the demon boar's ability to charm others as a special ability. Thanks!
I would be inclined to go with the text of charm person as a basis, which I just looked up and doesn't specify. That being said, for the purposes of players being charmed, it's pretty hard to pull one over on them, so it's probably best to just own up to the fact they've been charmed and not add the extra RP difficulty of having to pretend they don't know they were charmed, since they'll already have to roleplay actually being charmed.
I usually assume that creatures know they were charmed, or targeted for such. Charm can be very disruptive as it is; having the Charmed victim be unaware of the Charm would make it even more so.