I am not sure if there is direct flight from Kolkata to Shanghai, it seems no. I saw there is flights from Calcutta to Kunming. You can transfer to Shanghai then. Take Kunming-Shanghai Hongqiao flights and then change to bullet train from Hongqiao Railway Station to Yiwu. If you are arriving in Shanghai Pudong. There are two buses a day to Yiwu directly from the airport. You may also fly Delhi first then fly to Shanghai.