What books should I read to learn six hexagrams?

Qu Wei's "Detailed and True Six hexagrams"

Qu Wei's "Six Yao Multiple Images"

Qu Wei's Lecture Notes for Six Advanced Classes

Li Shunxiang's Six Mysteries

Six-year training courses in Li Shunxiang: elementary, intermediate and advanced.

Ancient Books: Poor Bao Tong's Bamboo Slips, Authentic Divination, Addition and Subtraction of Divination, Lecture Notes on Breaking Six Clues, and Li Hongcheng.