I have no idea how Jon is going to find out about his parentage but there is some magical power way beyond just dead Starks in the crypts at Winterfell. I think the crypts in part hold the key to my predicted relationship between the Starks and the White Walkers.
Like there was a pact and it was sealed in the crypts, or now with tat other epiosode I am thinking maybe the first White Walker was/is a Stark (the guy they shoved the dagger into) and that the Starks did this willingly to help the Children. I don't know. I just feel very strongly there is an ancient connection between white walkers and the Starks, that the loss of Winterfell in addition to the dragons is why the white walkers have gotten aggressive and gone rogue, and that whatever the connection is, Winterfell, and esp the crypts of Winterfell, are key to it.