If a Japanese citizen enters Shanghai and exits in 14 days to Hong Kong, can she reenter Shanghai

Yes, she can reenter Mainland China, Japan ordinary passport holders are exempt from a visa to Mainland China for up to 15 days per entry.

this is my last question after the marriage what are the neccessary document to acquire so my chinese wife have a japanese visa?

To appply for a Japanese visa, your wife has to prepare: a completely filled visa application form, a passport photo, her original valid passport, photocopy of her Hukou (Household registration book ) and your marriage certificate.

You have to provide Letter of Guarantee, citizen card, employment proof and taxi receipt.

BTW, Embassy and Consulate of Japan in China doesn't accept individual visa application, you have to apply for the visa through the designated visa agencies listed on the official website of the Japan Embassy.