1)- I need visa with multiple entrance? 2) Can I came back from Hong Kong to Brasil?

Hi, Hong Kong and Macao, as Special Administrative Regions of China, have their own visa policies which are different from China mainland. If you only enter mainland China once time, a single entry is enough. Because it is domestic trip from Beijing to Shanghai. And you will exit from mainland when you leave from Shanghai to Hong Kong. Of course, you can go back to Brasil from Hong Kong.