The books do more than insinuate that Jon is a warg. He is most definitely a warg. And so are all of his half-brothers and sisters. Arya instinctively skinchanges into a cat, for example, when she loses one of her other senses. The wildlings often regard Jon as a skinchanger, and Jon’s abilities are one of the reasons Qhorin Halfhand wanted him along with him. No trauma is necessary to awaken the abilities. They naturally have them. The abilities seem to be connected with the old powers awakening in the world again.

In the books, Jon has wolf dreams just like Bran does and he’s able to exert some limited control over Ghost while he’s sleeping. He also has the occasional prophetic dream. This connection they share is always there. Before climbing over the Wall with the wildlings, Jon sends Ghost back to Castle Black. While he directly tells Ghost where to go, subconsciously he most likely told Ghost where to go and how to get there as well. And sure enough, Ghost meets up with him again on the other side of the Wall.

In the show, only Bran is a warg.

How and why? really wanna know