read, study, pronounce
讀 centers on engaging with written text: reading, studying, or pronouncing words aloud. The meanings are closely linked as different aspects of interacting with writing.
讀 is the traditional form of 読. It combines 言 (speech) with 賣, which likely contributes the sound and may relate to the idea of reciting or reading aloud. The modern Japanese simplified form 読 replaces 賣 with 売.
The left side 言 (speech) and the right side 賣 (sell) suggest someone reading a text aloud to sell its ideas. Picture a street vendor reading a scroll to attract customers.
For ドク, imagine a doctor (ドク) reading a medical book to study: doctor -> ドク, and the doctor reads to learn.