There are two key pieces of Jon Snow's storyline that you need to remember before starting season seven. The first is that despite the fact Sansa has to ride in and save him and his army from their bloody, muddy failure in the Battle of the Bastards, Jon is the one crowned King in the North (which will likely have dire consequences for his relationship with Sansa).
The second is his true parentage. Thanks to Bran's flashback sequence, the long-held suspicion that Jon isn't actually Ned Stark's son/bastard is finally confirmed; Jon is the son of Ned's sister, Lyanna, and Rhaegar Targaryen. This means his claim to the Iron Throne is much stronger, but his hold in Winterfell is significantly weakened. Also, Dany is his aunt.
