There is no subdual damage in 5th edition.
The way to knock a creature out, according to the rules, is that you declare when they hit 0 hit points that you want to knock them out instead of potentially kill them.
I am going to make a small change to the rule. Currently, you get to declare kill or knock out when the target hits 0, after you have made the attack. I am going to change it so that you have to declare before you make the attack. In addition, I will not allow subdual in some circumstances and with some weapons.
