Indirect questions.

What for?
To sound more polite.
To beat about the bush (andarse con rodeos :P)

Common expressions used to "ask":

I wonder if...

I would like to know...

I don't know...

I'm not sure....

I don't remember...

Can/ could you tell me...?

Do you know...?

Do you have any idea...?

Do you happen to know...?

Word order
If we do not begin a question directly, but begin it with something like: Can you tell me...? Do you know...? I wonder if...? the word order is the same as in an affirmative statement (subject + verb).

Example:
Direct question: What is he doing? Indirect question: Do you know what he is doing?
Direct question: Where have they been? Indirect question: I wonder where they have been?

Do, does, did
If the direct question contains do, does or did, we omit it in the indirect question.
Example:
Direct question: What do you want? Indirect question: Can you tell me what you want?
Direct question: When did she leave? Indirect question: Do you know when she left?

Yes/no questions
In yes / no questions, we use if or whether and we have to change the word order.
Example:
Direct question: Have you seen my dog? Indirect question: Could you tell me if you have seen my dog?

Exercises:
http://www.usingenglish.com/quizzes/312.html
http://perso.wanadoo.es/autoenglish/gr.inqu.i.htm
http://www.oup.com/elt/global/products/headway/intermediate/a_grammar/unit11/hwy_int_unit11_1/
http://perso.wanadoo.es/autoEnglish/gr.inqu.p.htm