So far the only way I've found to take people down without killing them is Sleep Darts. None of my skills (that I've noticed) seem to be able to knock people out/put them to sleep. I noticed the "parry" button is also "choke" but when sneaking up on someone and pressing parry I just block, I don't seem to choke them; I'm also unsure whether that's lethal or not.
What are all the ways to knock someone unconscious? There seem to be very few.
Best Answer
You can sneak up and choke them. It's the RB on Xbox (Holding X after choking will automatically pick up the body for you to hide it). It's non-lethal and will not increase the death count.
However, if the unconscious body falls down stairs, off a high platform/balcony/etc., into water, they can die and that will increase kill count. Other enemies can also found the unconscious body and be alerted to your presence, so make sure to hide them after knocking em out. Other than that, nothing to worry about.