What guidelines did John Paul II offer for preventing illegal immigration?
The short answer
The document usually meant is his message of July 25, 1995, "The Church and Illegal Immigration." Its full text is available from EWTN, and Jimmy Akin has written about it.
The source
The reference is likely to John Paul II's message of July 25, 1995, titled The Church and Illegal Immigration.
Where to read it
The complete text is available at EWTN, and there is an article by Jimmy Akin on it.