The Internet is apparently full of people who believe they can do a convincing Jon Snow. Jimmy Kimmel found several of these impersonators and let Kit Harington be the judge of their skills.
Nothing on Jimmy Kimmel's show is ever ordinary, so instead of reading classic Game of Thrones lines, he has the impersonators read mundane things like cereal boxes and shampoo bottles in the style of Jon Snow. The real Jon Snow appears to be quite impressed.
Personally, I suggest skipping to the third impersonator because he will wow you with several other Game of Thrones character impersonations. His Littlefinger imitation is spot on.
Thanks Jimmy Kimmel for being ever-entertaining, and thanks Internet for consistently being full of people with the weirdest skills.