Your employer needs to obtain an approved LMIA in order for you to be able to apply for a closed work permit tied to that specific employer. LMIAs are typically only approved for full time jobs. The LMIA process is quite involved and typically takes several months to complete. If your PGWP is expiring soon, the employer should kick off the LMIA process as soon as possible (first step is to advertise the job for at least a month to prove no Canadian could be found for the role). Again, you really want to be doing this for a full time position rather than part time.