The only way to obtain (Without Mods Or Commands) this creature (150 Level Fenrir) is by killing the Fenrirsulfr (Fjordur Boss).

Right after you kill the Fenrirsulfr, you will get your own fenrir in a cryopod in your inventory.

Dododex (Best ARK Wiki) might say that these Fenrirs are a knock-out tame, that is true but the problem is that these do not spawn in the wild, so i guess you use commands or mods to spawn them and tame them.

I hope this helped! Thank you!

-Pablo

More Fenrir Taming & KO Tips