Board Thread:Questions and Answers/@comment-24810520-20151013034255/@comment-27036174-20151013110035

According to the wiki, Dark Wisdom is a "special ability". So maybe in the New World, it would be something you're born with, and does not need a ritual. As for how Ainz got it himself, I don't know, but I would assume it was given to him after he maxed out a class or something, like his special skill "The Goal of All Life is Death".