Thank you, guillermooo.
The simplest way is to bring up the console and type:
CODE: SELECT ALL
then watch the output after pressing a key combination.
According your hint, I found [menu: View > Show Console]
and it shows detail of command.
Alternatively, .sublime-keymap files is where key bindings are defined.
You can look for those inside the Packages folder.
I can't find "Packages" folder under /Applications/Sublime\ Text\ 2.app/Contents/,
but I found that [menu: Sublime Text 2 > Preferences > Key Bindings - Default] opens