Players can submit questions to this reddit thread. Mojang will pick the best ones and address them live online – there's no specific time for the stream yet, but it will be archived. Mojang says to check the site for more info as it comes in.
"We're extremely grateful to all players for your dedication and creativity," Mojang writes. "Without that, Minecraft wouldn't be anywhere near as significant as it is today."
Minecraft recently passed 12 million sales on Xbox 360 and 14 million on PC. In its first month on PS3, Minecraft hit 1 million sales. In total, Minecraft has sold roughly 576 squidillion copies across all platforms.