More general censorship discussion at: Censorship (审查).
Examples of Zhihu censorship:
Ciro Santilli’s Zhihu purge 2019-11-03 (三西猴被知乎抹去)
Zhihu censorship of Hao Haidong (知乎审查郝海东)
Other discussions:
https://www.quora.com/How-strict-is-Zhihus-content-censorship
Zhihu questions related to Ciro Santilli (三西猴相关的知乎问题)