On earth, after all: 究竟 / 到底
副词 / adverbs
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
Subject + 究竟 / 到底 + question ?
In a question, 到底 (dàodǐ, spoken) and 究竟 (jiūjìng, more written) show impatience or a wish to know the truth: "on earth, exactly, after all".
The sentence must be a real question: with a question word, a 还是 alternative, or the V不V form → but not with 吗: ✗ 你到底去吗？ ✓ 你到底去不去？
到底 also has an affirmative meaning: "finally, in the end": 问题到底解决了 (the problem was finally solved).
Examples
这条新闻到底是真的还是假的？
Zhè tiáo xīnwén dàodǐ shì zhēn de háishi jiǎ de?So is this news actually true or fake?
究竟发生了什么事？
Jiūjìng fāshēng le shénme shì?What exactly happened?
你到底想不想看这个视频？
Nǐ dàodǐ xiǎng bu xiǎng kàn zhège shìpín?Do you want to watch this video or not?
Common mistakes
✗ 你到底喜欢吗？ → no 吗. ✓ 你到底喜不喜欢？
✗ 到底谁你是？ → ✓ 你到底是谁？ (到底 follows a normal subject; it precedes a question-word subject: 到底谁对？)