So the offer was made in 2017, meaning after the election, I guess under the probe in to Russian meddling.

It's really confusing then: If he know that he did not use Russia, acquiring that knowledge wouldn't help much since the next election is in 3 years, so it can't be used as a leverage, unless he wanted the information as an insurance to the probe being biased by DNC influence. If he did, why would he want to know the source? The only thing he would want to know if Assange have been contacted by democrat, or if that information were available to begin with.

Sure is a news that asks more question than it answers, and why was it even mentioned in a court in London?