Here are the requirements for opening up Argus:
- Do the Legion Intro up through opening up your class hall and selecting your first zone to quest in. (If you skip this, it may or may not cause issues with later quests. It’s safest just to do it.)
- Complete Uniting the Isles from Khadgar inside the Violet Citadel in Dalaran to open up world quests. If you’ve done it before on a character, you just need to turn it back in. If it’s your first character through Legion, you’ll need to get to friendly with each of the zone factions. (Use that breadcrumb quest you got from your Order Hall.) This quest requires level 45.
- Unlock the Broken Shore. Complete “Armies of Legionfall” and “Assault on the Broken Shore” from Khadgar on Krasus’s Landing in Dalaran. (You can use the skip dialog if you want.) You don’t need to complete any of the follow up quests.
- Pick up “The Hand of Fate” from Khadgar in the Violet Citadel and complete the chain until you’ve unlocked Argus.