"How to say 'sleep' in English?" is how you ask for the English translation of the phrase "睡觉用英语怎么说".
The English word for "睡觉" is "sleep". So, if you want to ask someone how to say "sleep" in English, you can simply ask, "How do you say 'sleep' in English?" or "What's the English word for 'sleep'?".
