试衣间在哪里？

You just say the phrase as it is. There is no need for complex grammar here. You can point to the clothes in your hand while saying it. This makes your intent even clearer to the shop assistant. If you want to be extra polite, add 请问 (qǐng wèn) at the beginning. It means 'Excuse me, may I ask?' It turns a direct question into a polite request.

Use this in any retail environment. This includes massive shopping malls in Shanghai or tiny boutiques in Beijing. Use it when you have found something you love. Use it before you commit to buying. It is perfectly normal to ask this even in high-end luxury stores. The staff expect this question and will usually point or lead you there.

Do not use this in open-air street markets where trying on clothes isn't a thing. In those places, you might have to 'guess' your size or hold it up. Also, do not use it if you are looking for a restroom. That is a different 'room' entirely! Using this in a restaurant would definitely get you some confused stares. Unless, of course, the restaurant is incredibly avant-garde and sells shirts.

Shopping in China is a massive social activity. Fitting rooms in big cities like Chengdu or Guangzhou are often high-tech or very stylish. Some even have special lighting for that perfect 'fitting room selfie.' In older or smaller shops, the 'fitting room' might just be a curtained corner. Don't be surprised if the assistant stays close to the door. They are there to help you with sizes, not to rush you!

You might hear people say 更衣室在哪里？ (gēng yī shì zài nǎ lǐ). This is a bit more formal and translates to 'changing room.' In very casual settings, you might just hear 在哪儿试？ (zài nǎr shì) which means 'Where to try?' Keep it simple with the standard version until you feel like a pro.