Smartforms and Sapscripts can be called/issued from "the system", for which some customizing needs to be in place. Of course an Abap can create it's own Sapscript or Smartform call, but the most commonly used forms are linked to actual output types (e.g. NEU) as defined on table TNAPR.
So: if you know the name of the Smartform or Sapscript and you would like to know how (where) it is used, check out the TNAPR table !
Sapscript forms are backed up by a driver program, which controls the sequence of elements to be called as well as which data is available at which point. The field PGNAM holds the report name, RONAM is the routine that starts processing on the Sapscript form and FONAM is the name of the Sapscript form.