The is the first time Snowden has actively participated in something of this nature since last June. The Q&A is scheduled for January 23rd at 3PM ET. You can tune in over at freesnowden.is tomorrow afternoon.
At the moment, Snowden is still in exile in Russia after traveling there from Hong Kong earlier this year and is still quite hesitant to give interviews of any kind (understandably so). Having said that, the whistleblower has become more open to speaking out as of late, having given quite a deep and involved interview just last month with The Washington Post and then appearing on UK television to give an alternate Christmas address pertaining to "indiscriminate surveillance."
He has recently dismissed claims that he is some kind of Russian spy during an interview with The New Yorker. Snowden says this "‘Russian spy’ push is absurd” and that "outlets report statements that the speakers themselves admit are sheer speculation."
The session will run for about an hour tomorrow, the public can submit questions via Twitter using the hashtag: #AskSnowden. Apparently his answers will appear later on freesnowden.is/asksnowden, so even though it is scheduled as a live Q&A, it is unclear whether or not Snowden will answers questions live as well or not.