returning Quagnoth from one's library

A player controls Nephalia Academy, and is playing with their hand and the top card of their library revealed.
( https://scryfall.com/search?q=%28ora...rid&order=name ,
https://scryfall.com/search?q=%28ora...rid&order=name )

A spell or ability an opponent controls causes that player to discard 1 Quagnoth and nothing else.
Via their Nephalia Academy, that player reveals the Quagnoth
and puts it on top of their library instead of into their graveyard.
If nothing else happens in the meantime, will the Quagnoth's
triggered ability still return that Quagnoth to their hand?


I imagine WotC would want the answer to be no, due to
"What if the library was interacted with while the trigger was on the stack?",
but I can't think of anything in the comprehensive rules that
would stop it from returning in the situation I described:

701.8c specifies "without being revealed", and 603.2f specifies "at no time visible to all players".

Based on your outline, I would expect Quagnoth to return to hand.
Nephalia Academy rulings state: When you apply Nephalia Academy’s effect, the card was still discarded. Abilities that trigger when a card is discarded will still trigger. So we know replacing the zone does not affect the trigger of Quagnoth.

Further, rulings on Quagnoth: If an effect of a spell or ability an opponent controls causes Quagnoth to be discarded, but Quagnoth moves from your hand directly to the Exile zone (due to Leyline of the Void, for example), the ability will trigger from that zone. It will return Quagnoth to your hand from that zone when it resolves. While not directly indicating the case, it suggests that even if the zone is replaced, it will trigger from the new zone.

If nothing happens between the trigger and it resolving, I can see no reason why it would not be in your hand.

If anything were to manipulate your library as you alluded to, then things would change.
401.6 If an effect causes a player to play with the top card of their library revealed, and that particular card stops being revealed for any length of time before being revealed again, it becomes a new object.

I'm sure there are some effects that can cause you to manipulate your library somehow without changing the top card, and it would be up the players to maintain gamestate, but in every case I can think of, if the Quagnoth trigger is on the stack and it is on top of you library and something makes you shuffle or rearrange or otherwise potentially change the top card of you library, it becomes a different Quagnoth card unrelated the trigger on the stack and you do not get the card into hand.