How to list all available .plist keys on a certain domain application by defaults command?
This is not a trivial task, if I recall correctly people run the strings utility at the command-line against an Application, and look for things that match a structure similar to com.domain.FeatureName. (com.apple.iTunes, ch.cyberduck.CyberDuck, com.panic.Coda, etc.)

The likely easiest way to manage these overrides is by a System Preferences Pane by the name of Secrets. Using this installs a Preference Pane into System Preferences, and gives you an interface into choosing an application and changing their settings to your particular preference.