to read a book / to study, euphemism used by gamblers to replace 讀書 since書 (book) is homonymous with the word輸 (lose), which is unlucky for gamblers [colloquial]
Definitions (粵典–words.hk)
動詞
即係讀書；由於「書」同「輸」同音，所以有啲人為免唔吉利而將「書」改做「贏」 refers to 讀書;literally: to read win; a euphemism used by gamblers because 書 "book" is homonymous with 輸 "lose"