The only purpose of journaling a LF is to avoid an index rebuild if the system abnormally ends. You can't do anything else with this information.
You can manually start journaling on a LF with STRJRNAP but it's generally better to let the system journal the LF as needed via SMAPP (EDTRCYAP).
As Virgile said, you journal the PF, every change to the data in the PF (directly or via a LF) will be in the journal.
The actual journal information are in the journal receivers (*JRNRCV objects), data is removed when the journal receiver is deleted.
Regards,
Damien
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Damien Ferrand
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