What are the three classics of Taoism? What are the Tao Te Ching and the Book of Changes?

This question is very profound. These three Taoist classics are Laozi's Tao Te Ching, Zhuangzi's Nanhua Ching and Liezi's Xu Qingjing.

You are talking about China's three classics, the Tao Te Ching of Taoism, the Book of Changes of Confucianism and Huangdi Neijing of Physicians.

Supplement: Yujing is a classic of Taoist Shangqing School (Maoshan School).

Similarly, Lingbao Jing is a classic of Taoist Shaoyang School (Quanzhen School).