On the Enlighten interface, go to the top of the screen and click the'Programming Mode' Button. You screen should look similar to this:

Right click on the fixture you would like to view the address of, and select 'View/Edit Start Channel' from the menu options.  

The pop up window below will appear, showing you the start channel.  The fixture properties window shows the Fixture name, Fixture Number, Fixture Start Channel, and Amount of channels used.