All players get to see which card you return to your hand.
16-03-2018
wotc
Because Haunted Fengraf's ability doesn't target any creature card, any creature card put into the graveyard in response to that ability may be returned to your hand.
16-03-2018
wotc
The creature card returned to your hand is chosen at random as the ability resolves. If any player responds to the ability, that player won't yet know what card will be returned.
Random a card of Magic: The Gathering (MTG), but you can also roll the D20 dice, random a Planeswalker, have fun with the random rules and more.