Ms.Thelma Roche, you can try to apply for a double-entry tourist visa for 90 days, but the final decision is up to visa officer. However, there is no meaning for you to get a double entry visa, if you find a job in Shanghai, you have to exit Mainland China to apply for China Work Visa(https://www.travelchinaguide.com/embassy/visa/work.htm) , you don't need to use your double-entry tourist visa to return to Shanghai. If you are afraid that you can't find a job in Shanghai during 30 days (tourist visa generally allows 30 days stay duration), you can ask for more than 30 days stay duration and make it clear on the application form and ask for the Visa Officer's approval when you submit your application.