Subject + Verb + 多久
多久 (duōjiǔ) is used to ask about the duration of time something takes or has taken. It typically appears at the end of a question or after the verb to inquire about how long an action lasts.
从这里到机场要多久?
Cóng zhèlǐ dào jīchǎng yào duōjiǔ?
How long does it take to get to the airport from here?
你学中文学了多久了?
Nǐ xué Zhōngwén xué le duōjiǔ le?
How long have you been studying Chinese?
做这道菜需要多久?
Zuò zhè dào cài xūyào duōjiǔ?
How long does it take to make this dish?