In order to get reputation with The Wardens, you can do either of the following actions:
1) Do World Quests. The Wardens have World Quests spread all over The Broken Isles, and a lot of them awards rep with The Wardens. You can hover over the World Quest to check which factions it awards rep with, so just complete as many of the Wardens World Quests as possible.
2) Complete the Vault of the Wardens dungeon. The endboss of the dungeon awards each player with +250 Wardens reputation each time it is killed, so this is a consistent way of farming rep with them.
The Wardens reputation rewardsThe reputation vendor for the Wardens is located on the north shore of the Isle of The Watchers. He sells the following items:
Trapped Treasure Chest Kit
Schematic: Reinforced Headgun Rank 3 (Engineering)
Schematic: Bolt-Action Headgun Rank 3 (Engineering)
Fledgling Warden Owl
Boon of the Bloodhunter
Shoulder enchant that allows the wearer to obtain Bloodhunter´s Quarry from corpses of their enemies.
Vantus Rune Technique: Star Augur Etraeus Rank 3 (Inscription)
Vantus Rune Technique: Spellblade Aluriel Rank 3 (Inscription)
Vantus Rune Technique: Cenarius Rank 3 (Inscription)
Drape of the Patient Hunter
Design: Twisted Pandemonite Choker Rank 3 (Jewelcrafting)
Schematic: Sawed-off Cranial Cannon Rank 3 (Engineering)
Schematic: Semi-Automagic Cranial Cannon Rank 3 (Engineering)