To ko one you need a bow or cross bow with narcotic arrows. Then you need to find one. Once you do that you find a rock that it cant get up onto to and hit it with a normal arrow. Once it comes at you, you need to shoot it with the narcotic arrows the put your choice of for in it the there you go.
It really is that simple though, they can't reach you or your flier on a big enough rock, so if you don't want to make a trap you can just shoot down from a rock or cliff once the carnos are dealt with. Be ready for a goose chase once it starts running.