What does Underground Assault reward?

Underground Assault gives a choice of Polar Gauntlets, Sable Wand, 3,700 experience.

Where does Underground Assault start?

Shoni the Shilent in Stormwind City offers it.

Its level has not been recorded yet; it shows once a player accepts it with the addon running.

No. The quest exists in Classic Era as well.

World of Warcraft: Forever · quest

A quest in World of Warcraft: Forever, offered by Shoni the Shilent in Stormwind City. Recorded by 4 players running the addon.

Level and objectives show once a player with the addon accepts the quest.

Item	Given	Item level	Vendor sell
Polar Gauntlets	as a choice	22	5s 57c
Sable Wand	as a choice	22	13s 99c

What does Underground Assault reward?: Underground Assault gives a choice of Polar Gauntlets, Sable Wand, 3,700 experience.
Where does Underground Assault start?: Shoni the Shilent in Stormwind City offers it.
What level is Underground Assault?: Its level has not been recorded yet; it shows once a player accepts it with the addon running.
Is Underground Assault new in WoW Forever?: No. The quest exists in Classic Era as well.

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