You have to have the blood moon passive unlocked in the wolf skill tree and have a skill point in. Then go to one of the wolf shrines (Bangkorai - daggerfall, The Rift - ebonheart and Reapers march -Aldmeri). You will see devour pop up when you look at someone who has not been gifted with either a wolf or a bat bite.

Its up to you if you want to ask them or just bite them. Also you can only do it once a week per character.

Pesonally I go to the shrine and just bite the first person that devour pops up on. If they want it, awesome, if not they can get it cured via the quest that you get as soon as someone bites you.

Source: me, my first character is a crown brought wolf, my second is via wolf bite when I was trying to find the shrine near the rift.