Check your cleanup settings to ensure it’s set to the number of days you require (chgclnup)
If it is a batch job that should produce a joblog regardless of error code, have a developer change the program to always produce one.
You can also check/change the logging level manually while the job is active or in the jobq (CHGJOB JOB(JOBNUM/USERID/JOBNAME) LOG(4 00 *SECLVL) LOGCLPGM(*YES)
Not all job logs are kept, depends on error conditions and logging rules.
Job logs are typically places in outq QEZJOBLOG
Job logs can be found with WRKJOB or WRKUSRJOB
If it’s for your current job you can try this:
4. Display spooled files