Subject + 在 + 哪里 / Verb + 在 + 哪里
哪里 (nǎlǐ) is a question word meaning 'where.' It is used to ask about locations and can appear at the end of a sentence in indirect questions, as in 它藏在哪里 (where is it hidden). It is interchangeable with 哪儿 in most contexts.
你知道最近的地铁站在哪里吗?
Nǐ zhīdào zuìjìn de dìtiě zhàn zài nǎlǐ ma?
Do you know where the nearest subway station is?
请问洗手间在哪里?
Qǐngwèn xǐshǒujiān zài nǎlǐ?
Excuse me, where is the restroom?
我不记得把手机放在哪里了。
Wǒ bù jìde bǎ shǒujī fàng zài nǎlǐ le.
I don't remember where I put my phone.