What do double quotes mean around a domain in `defaults`

The network library is intended for client computers bound to a network domain server. A domain server acts as a central repository for configuration information -- mostly user accounts, but also (among other things) mount records. Mount records tell the client computers to automatically mount a certain file server share point automatically. If you use this to tell all the clients to mount a particular share point on /Network/Library, then you can put Preferences, Fonts, etc folders inside that share point and they'll be automatically available on all clients in the network domain.

This used to be a common way to manage network clients in NextStep (the predecessor of OS X), but is very rarely used in OS X. There are better ways to do most thing now, like putting managed preference settings directly in the network domain. At this point, the network library is more of a historical artifact than anything else...

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.