Example sentences
nǐ你zhī知dào道lù路ma吗？
Do you know the way?
shéi谁yě也bù不zhī知dào道。
Nobody knows.
About this word
知 is "to know" and 道 is "way, path", so 知道 is "to know the way of something", the plain verb for knowing a fact. It is stative: 我知道, 我不知道, and it never takes 正在 or 在. Keep it apart from 认识, which is knowing a person or a character, 了解, which is knowing a subject in depth, and 会, which is knowing how to do something. 我知道他昨天没来.
The story behind the character
知
知 is 矢 (arrow) beside 口 (mouth). The mouth carries the meaning: speech, words. The arrow is there for the sound, and it brings a picture worth keeping anyway, something that flies straight and hits what it aims at. Xu Shen defined 知 as 词也, a saying. So 知道 is knowing that lands on target.
道
道 is 辶, the walking radical, with 首 (head) on top. A head on a road. Xu Shen wrote 道, 所行道也, "the road you walk." The meaning was the dirt path first, and only later the abstract Way. So 知道, to know, is built from a picture of walking a road with your head leading.