If I'm playing Diablo 3 without a mouse, how can I Identify items?
I am assuming you have activated Mouse Keys in the Accessibility Center.
The mouse emulation works works on the principle, that there are two mouse buttons and only one can be the active button at a given time.
The three upper right keys, /, * and -, are used to control the selection:
Pressing 5 presses the curently selected mouse button.
So, in your case, move over the item with the arrow keys, press -, and then 5 to identify the item.
Just tested this, it works in D3 (and most probably, in any game or application, too).
The menu key, which on desktop simulates the right button, does not work in Diablo 3 as a right button action.
This should work similarly on MacOS X.
If you're playing on a Windows machine using a standard keyboard there should be a "Menu Key" that looks like an arrow hovering over a menu - that emulates a Right click on your mouse.
If you're playing with a gamepad then the alternative keyboard shortcut is Shift+F10 so use that as a custom keybind.
(Untested in Diablo 3 so have your grain of salt ready)
If you're playing on a Mac using the touch pad, you have two options: you can use command-click to simulate a right click, or you can enable the two-finger right click in the options for your touch pad, in which case clicking with two fingers contacting the touch pad will give you a right click.