Xelian,
I went back and took a look at 5E to see if it helped with 6E rules.
What information do you get: I think you may probe for one piece of information per Complex Action (5E). In 6E, I might let someone look for a piece of information per major action (not including the spell, so you get the info when you cast the spell).
How fast does it work: I believe the first question/information is answered when you cast the spell.
Sustained: I believe it can be sustained but you would reroll each time to see how many net hits you received.
Subject knowing: 6E doesn't state it, but 5E says the person knows they are being probed but doesn't mean they know who is probing.
Subject drop resistance: I would say so, also you can cast decrease att. and lower their resistance.
Caster knowing: I would say cast should have an idea of how much resistance they are getting, but should now if the subject is using their whole dice pool or not.
Caster know hits: I have always played where the caster knows how many hits they get.
Reprobe: Assuming that is still an option in game, then yes.
Unconscious: My opinion, Yes, but give caster a significant dice pool pen. Because the person's brain isn't working normally (Dreams, knocked unconscious, exc)
Again, these are only my opinion and using 5E as a benchmark...which isn't always the case.
Regards,
Ludwig