What does Finding the Antidote reward?

Finding the Antidote gives Venomtail Antidote outright.

Where does Finding the Antidote start?

Kor'ghan in Orgrimmar offers it.

The quest log lists it at level 9.

Yes. Its quest id is not in Classic Era, so it is part of what Forever adds.

World of Warcraft: Forever · quest · level 9 · new since Classic Era

A level 9 quest in World of Warcraft: Forever, offered by Kor'ghan in Orgrimmar. Recorded by 3 players running the addon.

Pay shows once a player with the addon opens the quest.

Item	Given	Item level	Vendor sell
Venomtail Antidote	outright	1

What does Finding the Antidote reward?: Finding the Antidote gives Venomtail Antidote outright.
Where does Finding the Antidote start?: Kor'ghan in Orgrimmar offers it.
What level is Finding the Antidote?: The quest log lists it at level 9.
Is Finding the Antidote new in WoW Forever?: Yes. Its quest id is not in Classic Era, so it is part of what Forever adds.

What sells at this level, and what to keep from these rewards, is in the level 1 to 10 gold guide.

Source: what players running the addon saw in the quest windows; the quest text itself stays in the game. Every quest seen · Orgrimmar