Several parts combine into one character.

Phonetic-semantic compound: 言 (speech / words) + 賣 (to sell, with the deeper sense "to bring out and display"). The encoding: bringing out the words written on a page through speech — i.e., reading aloud. Originally all "reading" was vocal — silent reading is a much later cultural development.

Three forms: 繁體 讀 / 新字体 読 (賣 simplified to 売 then to 売-form) / 简体 读 (right side abstracted to 卖). Of all three, the traditional 讀 best preserves the etymology.

Mandarin: dú, rising 2nd tone. 读书 (dúshū, read books / study), 读者 (dúzhě, reader), 阅读 (yuèdú, reading / to read intensively), 朗读 (lǎngdú, recite aloud), 默读 (mòdú, silent reading). The Chinese verb-object 读书 means both "literally read books" and metaphorically "go to school / study" — the act of reading and the institution of education are tied together.

Japanese: TWO on-readings split by usage. ドク (doku) is dominant — 読書 (dokusho, reading), 読者 (dokusha, reader), 読解 (dokkai, reading comprehension), 音読 (ondoku, on-reading — Sino-Japanese pronunciation), 訓読 (kundoku, kun-reading — native Japanese reading). Less common トク (toku) in 読本 (tokuhon, primer / textbook). Kun-reading よ.む (yo.mu, to read) is the everyday verb — 読む (yomu, to read), 読み (yomi, reading / pronunciation of a kanji).

音読 / 訓読 are essential vocabulary for Japanese learners themselves: every kanji has both an on-reading (Sino-Japanese, borrowed from Chinese) and a kun-reading (native Japanese). The terms naming this distinction use 読 itself.

Memory aid: words being brought out through the mouth — reading is speech making text audible.