How can I review the current keyboard bindings in a running instance of the Atom text editor
You can find the full set of current keyboard shortcuts in the Settings View:
Another way you can find keybindings is if you want to know what a particular key does, you can open the Keybinding Resolver view:
This view is also very useful for situations where you want to be sure that Atom is receiving the key combination you're pressing correctly.
The issue with the Open Your Keymap
command is that it only shows you your personal overrides of the keybindings that the Atom application already has. It does nothing to tell you the full set or even if your keybindings are being used in a particular situation. That's what the above techniques are for.