The Ghost ability Possession (Recharge 6) gives this guidance:
The ghost now controls the body but doesn’t deprive the target of awareness. The ghost can’t be targeted by any Attack, spell, or other Effect, except ones that turn Undead, and it retains its Alignment, Intelligence, Wisdom, Charisma, and immunity to being Charmed and Frightened. It otherwise uses the possessed target’s Statistics, but doesn’t gain access to the target’s knowledge, Class Features, or Proficiencies.
It is unclear to me if Feats counts as a thing they do not gain access to.