You can make the diagnostic output available as an option to anyone who invokes your CLIST. To do so, code a keyword parameter such as DEBUG on the PROC statement as follows:

PROC 0 DEBUG
IF &DEBUG=DEBUG THEN + 
CONTROL LIST CONLIST SYMLIST MSG

The CONTROL options take effect when you invoke the CLIST with the DEBUG parameter, for example (explicit invocation):

EX clistname 'DEBUG'

or, implicit invocation:

%clistname DEBUG