If you haven't received degree completion letter from the school, and if your study permit is still valid, then you can work according to the conditions of your study permit (possibly not full-time, only part-time unless it is a scheduled break term.). When you receive your degree completion letter, you should stop working, submit your PGWP application and then resume working if you satisfy conditions that permit you to work while waiting for PGWP application to be approved (e.g. having a valid study permit, not working more than allowed time during study, etc.).