By default, the Compiler looks for copybooks in the same directory as the program using them. If your copybooks are elsewhere, you need to define their location.
Each COPY statement in your program identifies a copybook to be copied. If the filename in the COPY statement is incomplete, because it lacks either an extension or a path, the Compiler searches for it as follows:
If the COPY statement does not give the extension of the copybook's filename, the Compiler searches for files with extensions given by the directive COPYEXT.