I work for a reputed bank as a PO, it is possible to do CA without quitting the job? If possible, please explain how?

We all know that CA is the toughest exams. So, I sincerely suggest you that, yes, it's possible to do a job and pursue CA simultaneously.

No, CA requires full attention. I would like to suggest you that continue your job and try to clear 1 level for CA then you can decide what to pursue either your job or your passion.