If You will create db2 connection on IBMi , QSQSRVR job will be created under QSYSWRK subsystem with specified user.
You can ensure it with using db2_pconnect() function.
For example, db2_pconnect('*LOCAL', 'TESTUSR', 'PASSWORD') will bring us QSQSRVR job with TESTUSR user.
If You omit the user, IHS default user is used in the job.