Various Pro Tips
Database viewer
Android - you can use the new App Inspector in modern versions of Android Studio.
Via Flipper You can also use Facebook Flipper with a plugin. See discussion.
iOS - check open database path in iOS System Log (via Console for plugged-in device, or Xcode logs, or by using find), then open it via sqlite3 in the console, or an external tool like sqlitebrowser
Prepopulating database on native
There's no built-in support for this. One way is to generate a SQLite DB (you can use the the Node SQLite support in 0.19.0-2 pre-release or extract it from an ios/android app), bundle it with the app, and then use a bit of code to check if the DB you're expecting it available, and if not, making a copy of the default DB — before you attempt loading DB from JS side. See discussion