To make the computer nuke, two things are required: the computer must have both a loaded nuke silo and a ghost. So first, either preplace a nuke silo and ghost, or create them using triggers. The computer should also be allied to all players because they will auto target any enemy units and ignore the location specified to nuke, when the AI script 'Al Nuke Here' is executed.
This trigger will load the nuke silos.
-Execute AI script 'BW Terran 2-A Fill Silos With Nuke (Type 1)' at '(Location where nuke silos are located)'.
This trigger will tell the ghost to nuke a location.
Execute AI script 'AI Nuke Here' at 'Location to Nuke'.