by processing the system log : each job when terminates has a message into the system log.
here the challenge is to find the API that retrieve the system log as do DSPLOG
If you want job processing time info, you have to track it. You can process the history log as noted above. It’s not trivial and takes some practice to learn its quirks.
The system function to track this is job accounting. Read the Information Center section on Managing job accounting and review the surrounding sections from the navigation pane on the left-hand side of that page.
If you want to know processing time of “a” job today, you’re going to want to know the processing time used between noon and 1:00 PM next week. Or you’ll want to know how many transactions were processed. Whatever you want will be more easily available if you set it up ahead of time.