I think the nearest Jon Snow has as an antithesis in Game of Thrones is Daenerys Targaryen. An antithesis is someone who is an opposite of another person. It is meant to provide contrast. It's light versus dark, black against white, good versus evil. In this respect, Daenerys is his antithesis in terms of their circumstances, their personalities, and their ambitions,

So, where Jon Snow was reborn from ice, Daenerys Targaryen was reborn from fire. Where she is constantly seeking her destiny, trying to get to the Iron Throne, he always tries to shy away from it more content to just serve a rightful ruler. Where she doesn't not bat an eye when it comes to defeating her enemies, he has more compassion even for those he is supposed to loathe. And, where she is always so sure of herself, her identity, and what her path moving forward is, he is always hesitating, he has no knowledge of his parentage, and he is often just reacting to things being thrown his way.