When learning a new language and practicing it with native speakers, you often need to indicate your knowledge of the topic. In Mandarin you use zhīdao (know) and bù zhīdào (don’t know).

Zhīdao is made up of two characters: 知道. The first character 知 (zhī) means "to know,” or “to be aware” and the second character 道 (dào) means “truth,” or “principle.” Dào also means “direction” or “path” and in this context it forms the first character of “Daoism” (Taoism).
Examples of Zhidao

    Qǐngwèn, sheí zhīdao nǎli yǒu yóujú?
    請問, 誰知道哪裡有郵局?
    请问, 谁知道哪里有邮局?
    Excuse me, does anyone know wher the post office is?

    Wǒ bù zhīdào.
    我不知道｡
    我不知道｡
    I don’t know.