If you want to ask where something is located you can say: sth 在哪儿（在哪里，means where）？ 例：你家在哪儿？Where is your home? (Question) This is correct. But how do I say I don’t know where something is located? 我不知道在哪儿地铁。（this is wrong.）I don’t know where the subway is. (Statement) This one you should say: 我不知道地铁在哪儿。 I think you could use 在哪儿 easily in this pattern. eg: something 在哪儿 or 在哪里？ or 我不知道something在哪里。You could change something into what you want to change. like museum博物馆, supermarket超市, park公园 etc. You could change something into what ever little places or big places. For exmple: 1. 博物馆在哪里？ 2. 超市在哪里？ 3. 公园在哪里？ 1. 我不知道博物馆在哪里。 2. 我不知道超市在哪里。3. 我不知道公园在哪里。 Hope these can help you.

Yep. Indirect questions in Chinese are nice and easy. You just but 我不知道 before the original questions. There is no change in the word order.

You are right.”在哪儿“ can be used as both statement and question as your examples showed. BUT "I don’t know where the subway is" in Chinese is "我不知道地铁在哪儿。“