• Q: How do I find out, in which file(s) a predicate is actually defined?
• A: This can be simply done by using the built-in predicate_property/2 with the property file(FileName).

/* * * * predicate_in_file(Head, File) * * * * 
 * 
 *  Example:
 *   ?- predicate_in_file(Head, 'd:/workspaces/runtime-eclipseapplication/pop/qap.pl').
 *   Head = predicate_in_file(_, _) ;
 *   false. 
 *
 */

predicate_in_file(Head, File):-
  predicate_property(Head, file(File)).

Note: In case of “multifile” predicates (whose clauses are unioned from the contents of multiple files) the above gives the name of just one file, not of all If you don't know what multifile predicates are and how to work with them, see the SWI-Prlog manual¹⁾.

• listing(my_predicate/3) gives me the implementation of my_predicate with 3 parameters.