jiū jìng
大家都想知道个究竟。
dà jiā dōu xiǎng zhī dào gè jiū jìng.
Everyone wants to know the truth.
究竟是怎么回事？
Jiūjìng shì zěnme huí shì?
What exactly is going on?
你究竟答应不答应？注意是非问句（如“你答应吗？”）里不用“究竟”。
Nǐ jiūjìng dāying bù dāying? Zhùyì shìfēi wènjù (rú 'nǐ dāying ma?') lǐ bù yòng 'jiūjìng'.
Will you agree or not? Note that 'jiujing' is not used in yes-no questions (such as 'Will you agree?').