In VS Code, how can I get a keybindings.json with all the default shortcuts?

Vscode keybindings.json gets generated only when you change at least one keyboard shortcut, to save only the modified keys, at %appdata%\roaming\code\user.

How can I get the default keybindings.json file? with all the default keyboard shortcuts?

For version >1.34.0,

1. Click File > Preferences > Keyboard Shortcuts
2. There is a triple-dot (...) at the top-right hand corner. Click on that. (the More Actions menu)
3. Select "Show Default Keybindings".

you can also refer to: https://code.visualstudio.com/docs/getstarted/keybindings#_viewing-modified-keybindings

or,

you can probably refer to https://github.com/codebling/vs-code-default-keybindings