How do you say where is the bathroom in mandarin?

There are a couple of ways to say "Where is the bathroom?" in Mandarin, depending on the formality of the situation:

Formal:

* 洗手间在哪里？(Xǐshǒujiān zài nǎlǐ?) - This is the most common and polite way to ask.

* 请问，洗手间在哪里？(Qǐngwèn, xǐshǒujiān zài nǎlǐ?) - Adding "请问 (qǐngwèn)" makes it even more polite.

Informal:

* 厕所在哪里？(Cèsuǒ zài nǎlǐ?) - This is more casual and can be used with friends or family.

Note:

* "洗手间 (xǐshǒujiān)" literally means "hand washing room" and is a more formal term for bathroom.

* "厕所 (cèsuǒ)" literally means "toilet" and is a more casual term.

You can also use gestures, like pointing to your bladder, if you are unsure how to say it.