Heh, R+L=J finally comes to the Trekbbs. What next, "Who killed Asmodean"?
The people who might know of Jon's true parentage are actually more numerous than is commonly thought.
Varys, obviously. The Spider was around back then.
Littlefinger, might have figured it out.
Barristan, might know, yet have blocked it out.
Jon Connington, presumed dead, but as the Hand of Aerys and Rhaegar's best friend would perhaps have known of Jon. It has been speculated that he is alive and is the Griffon in the Free Cities.
Ashara Dayne, she was an intimate of Elia, Rhaegar, Ned and maybe Lyanna. We're told she threw herself off a cliff, but it has been speculated that she is alive and following Danaerys as the shadowbinder Quaithe.