Companion Training System
Note knowledge of this system should be treated as in character in game information (akin to crafting recipes). You are free to share basic information in character post but do not divulge any taming or training techniques in the forums or on this wiki.
There are a handful of books in game on the various aspects of Companion training (The ranger written books may not be useful for they speak of a different set of techniques)
There may be creatures in the world that refuse to ever be tamed but more likely the knowledge to tame was lost and just needs to be discovered again. If you have attempted to tame such a creature and you have exhausted all known knowledge you may start on a quest to research the needed knowledge. Look to the wandering elder druids of this world ... I am told there are some waiting to help those willing to take on such a quest if you are willing to share this information once the quest is completed.