The Spiderfan web site is a fan web site. It's not official.
It's never been revealed in any comic story what the "J" in J Jonah Jameson stands for. It might be John, but there's never been any indication that Jonah's son shares the same name as his father. It might not stand for anything, being just an affectation that Jonah adopted early in his career. In the 90's cartoon they implied that it stood for "Jigsaw", a nickname Jonah earned during his reporting days, but that's never been reflected in the comics.
The J is like the face of Doctor Doom. It's something we are meant to ponder, but never be given a final answer to.