The application needs to provide a keyword list (SJRELIST) to the RETRIEVE service. The keyword list contains paired fields; each pair consists of a keyword field and a pointer field. In the list, the application specifies the JCL keywords for which information is to be retrieved. For each keyword specified, the RETRIEVE service returns a pointer to the text unit pointer list associated with the keyword.
The SJFREQ macro description in z/OS MVS Programming: Authorized Assembler Services Reference SET-WTO shows the SJRELIST paired fields and their offsets and lengths. The description indicates the fields that the application must initialize.