The Permanent Representative of China to the UN has deposited the country's instrument of accession to the treaty to Secretary-General Antonio Guterres.
So one of their first acts would have to be extending or rescinding Article 50, delaying or even stopping Brexit when people want us to get on with it.
There are probably small scale things that North Korea might request behind closed door, but ultimately, North Korea would be speaking things like a peace treaty with the United States and South Korea.
The first British embassy was sent to China in 1792, and it aimed to negotiate a treaty of friendship and commerce between George III and the Emperor Qianlong.