1. Verbs that require prepositions
Who did you talk to on the phone?
To whom did you talk...? 
Where are you staying at in London?
At where are you staying...? 
What are you thinking about?
About what are you thinking? 
Where is she from?
From where is she? 

2. Wait a minute! Metallica has a song called “for whom the bell tolls”!
 That is not a question;
 It should be understood as “those/the people for whom the bell tolls”
 That is a book by Hemingway, first and foremost

3. Question words as subject
In present simple and past simple questions, when the question word is the subject, you shouldn’t use do/does/did

4. Question words as subject
Who does she love?
Who loves her?
Which footballer do you admire the most?
Which footballer scored the most goals in World Cups?

5. Question words as subject
How many people did you invite to the party?
How many people came to the party?
Who did you send the postcard to?
Who sent this postcard to you?

6. Indirect questions
Use indirect questions when you want to make polite questions (when you are talking to people you don’t know very well)

7. Indirect questions Could you tell me...? Do you (happen to) know...?
I wonder...
I wonder if you could tell me...
Would you mind telling me...?

8. Indirect questions
 Word order changes, i.e., reported questions are organized like statements, not like questions. Do/does/did disappear.  In yes/no questions, you have to insert if or whether.

9. Indirect questions  “Where does she live?”
Could you tell me where *** she lives?
“Are they from Rio?”
Do you know if they are from Rio?