If the us dollar declines, how are stocks in china affected?

There is a multitude of factors that can happen, but given that most companies in china listed exchanges have businesss in china, a decline of US dollar may negatively afffect their exports to USA and in turn their profits

Usually when a foreign company is listed in US. Or can be a local company and listed in US. Then when US dollar declines, the share price do react. But the business itself doesn't really affect much. It depends on how much exposure the business has in the US.