"J Dawson's" gravesite is located in Halifax - in the aftermath of the movie, it became a bit of a focal point for pining di Caprio fans. However, at that time, Dawson's real life was so obscure that not even his first name was known...indeed, it was stated by some prominant people in Titanic circles that the 'J' stood for 'James'.
It was Senan who discovered the story behind the name...and, indeed, it was he who discovered the name! (Joseph). There was work done by other researchers as well, it should be noted, but the bulk of research was done primarily by Molony. He published some of his findings in his 2000 book The Irish Aboard Titanic and then later in the article on this site and in the documentary. His research does predate publication, of course - I could ask him when exactly he came across the story.