Subject + 究竟 + Question Word + Verb
究竟 (jiūjìng) is an adverb used in questions to express strong emotion or insistence, similar to "on earth" or "exactly" in English. It intensifies the question, showing the speaker's frustration, curiosity, or demand for a clear answer.
你究竟想要什么?说清楚。
Nǐ jiūjìng xiǎng yào shénme? Shuō qīngchu.
What exactly do you want? Say it clearly.
这件事究竟是谁干的?
Zhè jiàn shì jiūjìng shì shéi gàn de?
Who on earth did this?
他究竟去了哪里?谁都联系不上他。
Tā jiūjìng qù le nǎlǐ? Shéi dōu liánxì bú shàng tā.
Where on earth did he go? Nobody can reach him.