Is Multi engine rating is necessary to have a Commerical Pilot Job !? Or Single engine rating will work ?
It depends on the country in which you want to work as a commercial pilot. Technically single engine rating is enough but Pilots pick up Multi engine Training to fly faster and higher. And multi engine rating is mandatory if you want to work as a pilot in any of the airlines. So if you already have a commercial pilot certificate, you just need to obtain the necessary training for Multi engine rating.