From what I could find, the PMBOK is an IEEE standard, but it cannot be said that “IEEE has a PMBOK”. A Google search for “IEEE's PMBOK”, “IEEE's Project Management Body of Knowledge”, “IEEE PMBOK” and “IEEE Project Management Body of Knowledge” all returned few (and irrelevant) hits.
So, I think neither of your sentences is appropriate. The best that can be said, as far as I understand, is that “PMBOK is an IEEE standard”, or to “IEEE’s PMBOK standard”. I'd be happy to revise that opinion if more context was provided, of course!