This word riddle asks a strange question: where does today come before yesterday? In normal time, yesterday always comes first, so the clue clearly is not talking about a calendar or the order of days.
The answer is the dictionary. In a dictionary, words are arranged alphabetically rather than chronologically. The word “today” appears under T, while “yesterday” appears under Y. Because T comes before Y in the alphabet, “today” appears before “yesterday” on the page.
That simple switch from time order to alphabetical order is what makes the riddle work. It is a good example of how many riddles depend less on difficult knowledge and more on noticing that a familiar word can be interpreted in a different way.
