How do I fight Odin?

[Kargath]

In Vile Peaks 10 AF when I examine the shadowy thing it just says "There is a strong energy source in the area."

[Sage]

you need to go to vile peaks 200 af to start the quest chain and do it until he unlocks.

[*Logan*]

...and you unlock Vile Peaks 200 AF from The Archylte Steppe with a Wild Artefact.