A plot diagram is a useful tool to help show the main bits of a story. The reason why a plot diagram is so helpful is because it usually quite brief. In regard to your question about how much info to put into the diagram, put the most basic and important details. You can use complete sentences, but I prefer bullet points listed under each portion of the diagram.
If your teacher is asking for a standard plot diagram, it is going to have five parts. They are as follows: introduction/exposition, rising action, climax, falling action, and conclusion.
For the introduction of your diagram, include the setting information. The story takes place in Muji, China. Include information on the most immediate and important characters. I would only include Chiu. His wife is not important to the story. Include info about his job and reason for being in Muji. Also include the info about his hepatitis.
Rising Action: Chiu's arrest is good for this. I would also include the detail about how he's asked to sign a false confession. Lastly, include the info about his hepatitis symptoms returning.
Climax: Fenjin's torture and Chiu signing the false confession.
Falling action: Chiu and Fenjin having tea at multiple places in Muji.
Conclusion: The hepatitis outbreak in Muji a month later.