Every individual job on the AS400 has its own QTEMP library.
Two sessions with the same ID are still two separate jobs so each will have its own QTEMP.
“suppose we have one session and two jobs” – ? I don’t understand what you mean here. If you mean 2 batch jobs submitted from the same session, then my first answer applies as they are 2 new jobs and each will have its own QTEMP.
In short it is not possible for multiple jobs to share a QTEMP library.