Yes, this is on the fence. This is known in the series as a “journal” but by all accounts it’s a commonplace book.
For those of you who aren’t fans of the series (where have you been?), the protagonists, Sam and Dean Winchester, travel the US fighting all sorts of supernatural monsters. Much of the information they find about these monsters is from their late father’s journal, a ring-bound folio full of clippings, photos, drawings and descriptions.
I have created a page on this blog about commonplaces in fiction and this journal may seem to violate the “if I shake it does anything fall out?” rule. But you can see this folio was meant to be used ‘on the road’, with all the random clippings carefully bound or glued in place.
Also, although much of it is personal diary entry, this seems to have been common of historical commonplaces. There is not a clear distinction between diary and commonplace book. The important fact of this particular journal is that it’s a tool to be carried, referenced and used by Sam and Dean, not a private diary to be stuffed under a mattress.
Check out the Supernatural wiki page for an overview of this journal: http://supernatural.wikia.com/wiki/John_Winchester’s_Journal
Or, for an intensive (and slightly disturbing) journey, check out this site which outlines one fan’s creation of John Winchester’s journal as faithfully as shaky stills from the show will allow http://creatingjohnwinchestersjournal.tumblr.com/