Where is the bank? is a DIRECT QUESTION.
Do you know where the bank is? is an INDIRECT QUESTION. It is a polite way of getting information.
Could you tell me how much it costs? (NOT does it cost)
Do you know where the toilets are? (NOT are the toilets)
Can you ask him when we can leave? (NOT can we leave)
Could you tell me what they are doing? (NOT are they doing)
Could you tell me if the flight from New York has arrived?
Do you know if the flight to New York has left yet?
She wants to know when the course begins. (NOT does ... begin)
He wants to know where he can smoke. (NOT can he smoke)
Here are some more statements with question words:
I can't remember where I have put them. (NOT have I put)
I'd like to know what you saw there. (NOT did you see)
They haven't decided where they will go. (NOT will they go)
What a beautiful day it is! (NOT is it)
Look how fast they are going! (NOT are they going)