It means "it seems like most people don't know what facebook is, but you would expect that Zuckerberg knows. But we guess even he doesn't know it".

that works with a negative 'doesn't know it' but not with a positive 'does know it'.

The question does even X know Y? Implies that X is somehow out of touch, and not knowing Y, but maybe they do - surprise!

The question Does even X not know Y? Implies we would expect X to know Y, but what if even X does not?

The question Doesn't X even know Y? Implies that X is stupid and doesn't know a lot of things, but can it be that they are so stupid that they don't even know Y!?!?

On edit:

The question Does X know even Y? Implies they are knowledgable about a lot of things, but Y is such a rare and mysterious subject that we would be surprised if they did but what if they do know Y!?!

There are a lot more nuances than your analysis admits, and one is the assumed inflection of the speaker.

Consider "Does anyone know Y?". Depending on how it is said, it could be either a straightforward question about whether anyone knows Y, or with an upward inflection on "anyone" it could mean "I doubt anyone knows Y, but it's possible someone does."

With that same inflection on a person's name, "Does even Person know Y?" has the same meaning as your "Does even X not know Y?"

Perhaps, although I had a difficult time hearing the inflection when reading the headline.

It's the correct way to state what they mean to state ('not even Mark Zuckerberg knows what Facebook is' rephrased as a question). But certainly not an elegant or easy-to-read headline - I choked on it too. Reminds me of that old copy-pasta: 'Has Anyone Really Been Far Even as Decided to Use Even Go Want to do Look More Like?'

No - it's specifically relating to him, not his knowledge.