知之為知之，不知為不知 [－－为－－－－－为－－]

Jyutping zi1 zi1 wai6 zi1 zi1 ， bat1 zi1 wai4 bat1 zi1
Pinyin zhī zhī wéi zhī zhī ， bù zhī wéi bù zhī

Definitions (Wiktionary)
  1. proverb
    You either know it or you don't (don't pretend to know it if you don't).