To make a trigger in photoshop, you put the letter at the end of the name in parentheses, like (A). That means that layer will only show up if you press that key.
To make it hide everything else on the same level when it's triggered, add an exclamation mark, like (A!).
You'll need to select a layer in the Puppet Panel inside CH to have keyboard trigger options.
This part of this video might help, showing different key triggers for hands: https://youtu.be/H4J9tKuibVk?t=36m18s
Ah - looks like you're using Preview 1 (see the top toolbar). You'll need to update to a later version by updating your After Effects to see triggers inside CH.