This is one of the most useful phrases when traveling in Thailand.

Say:
ห้องน้ำอยู่ที่ไหนคะ/ครับ
Hong naam yoo tee nai ka/krub
“Where is the restroom?”

If someone helps you, you can reply:
ขอบคุณค่ะ/ครับ
Khob khun ka/krub
“Thank you.”

This phrase is useful in restaurants, shopping malls, temples, cafés, and airports.

Practice slowly and clearly. Thai people will appreciate your effort.