Is it possible to study in China without knowing Chinese? Is it possible to enroll into and complete a graduate school in China while having only English language skills, without speaking Chinese at all? In particular, I am interested in (theoretical) physics.
If you include Hong Kong as part of China, the answer is Yes but limited to Hong Kong. English is an official language of Hong Kong. Universities in Hong Kong all use English as the media of teaching and the common language for research is English. No Physics courses are taught in languages other than English and no faculty members are not proficient in English. See this official website for reference. The best are University of Hong Kong, The Chinese University of Hong Kong and The Hong Kong University of Science and Technology.

Otherwise the choices are limited to those high-ranking universities in China such as Peking University and Tsinghua University. In Tsinghua, most faculty members use English for publication purpose but not at all for communications in research. Most teaching and administration stuff are in Chinese. So you have to learn chinese at least in conversational level to survive a Phd there.