Did they leave me a message? // Would you please tell me...
Would you please tell me if (or whether) they left me a message?
Do they serve breakfast in the rooms? // Can you tell me...
Can you tell me if (or whether) they serve breakfast in the rooms?
Have they already left? // Could you tell me...
Could you tell me if (or whether) they have already left?
Where is the library? // Would you tell me...
Would you tell me where the library is?
What time does the bus leave? // Do you know...
Do you know what time the bus leaves?
How long will it take? // Do you know...
Do you know how long it will take?