Is it possible to create a keyboard shortcut to open Developer Tools on on Google Chrome on a Mac?
Ctrl-Shift-J does it on Linux and Windows.
I think most Keyboard Shortcuts are listed in menus, when applicable.
Also...you can often define your own custom keyboard shortcuts in OS X by going to System Preferences > Keyboard & Mouse > Keyboard Shortcuts, then Adding a new shortcut that matches the name of the menu item you want to access. See full instructions at Apple Mac OS X 10.6 Help.
If needed, Apple Keyboard Symbols has a good rundown on which symbols match which modifier keys. Also, I always remember the ALT/Option key because it's symbol shows an 'alternate' path: ⌥