I believe you mean Command Z (Undo)?
If you use the default U.S. Preset of key commands, Option + Command + Z opens your undo history, so that you can see (and monitor) the history of edits you've recently made. You can also choose Edit > Undo History to open your undo history window.
Below, you can see that when I move a MIDI note, an action called 'Move events' is added to the undo history, and when I click the Undo button, the MIDI note goes back to its original position.