At least as much as he knows, or will admit.
He made to statements this morning on ABC which I think bear up under what we know from the reportage.
First, about Snowden:
Our legal people have been in contact with Mr. Snowden. I can't say anything about the present situation.
He doesn't say when he has had contact with Snowden, but we know that Wikileaks people delivered the Ecuadorean passage to him in HK allegedly for his flight to Quito via Moscow and Havanna. We know he ended up in Moscow and was booked to Havanna. No problems yet.
We know that Assange likely got the transit papers from the London counsel and delivered them to HK via a Wikileaks courier who would then accompany Snowden (Sarah Harrison?).
Then, when Snowden does not board the Havanna flight we now know something has gone askew.
Furthermore, the USA has cancelled his passport and now Ecuador is denying the safe passage papers that got him to Moscow.
The Snowden father business adds one more piece of info. Assange says this on ABC today:
Mr. Snowden's father as a parent, of course he is worried in this situation, every father would be worried in this situation. We have established contact with Mr. Snowden's father's lawyer to put some of his concerns to rest.
So it very much appears from this that Assange has remained in fairly recent contact with Snowden. How else could he provide such insurance? (There are undoubtedly reporters who will check this Assange-Snowden family contact.)
I think Snowden's still in the transit zone at Sheremetyevo.