Interrogation

There are four ways of forming French interrogatives.

Do you speak French?

• Vous parlez français?

All that changes here is raising of the voice at the end of a statement. When speaking, intonation is incredibly important, so in this case just changing the tone of your voice indicates a question. This is one of the simplest ways to make a question. However it is ONLY used when speaking

• Parlez-vous français?

Another common question form is to invert the verb (parlez) and the subject (vous), as in parlez-vous?

A hyphen is used between the verb and the subject.

An extra –t- is added between the verb and the pronoun when the verb ends in an -a or -e.

e.g. Parle-t-elle français? - Does she speak French?

Also, in the plural, the t must be pronounced:

Parlent-ils français? - Do they speak French?

(Normally, the –ent would be silent, but in the inverted question form, the t is pronounced).

In the simple past tense (passé compose), it is the avoir or être verb that is inverted, not the past participle.

e.g.

A-t-il habité en France? - Did he live in France? 

As-tu reçu la lettre? - Did you receive the letter?

• Est-ce que vous parlez français?

Est-ce que is a phrase used in front of a sentence to make it a question, the same way we use “Do” in English. Note the word order stays as normal.

• Vous parlez français, n’est-ce pas?

Add the tag n'est-ce pas? to the end of the sentence. It is like the negative - isn't it?, doesn't it? in English.

French Interrogative vocabulary - using question words. 

You can also ask questions by using French interrogative adverbs. Remember to invert the verb and the subject:

Où - Where? 

Où est la bibliothèque? - Where is the library?

Quand? - When? 

Quand as-tu reçu la lettre? - When did you receive the letter?

Comment? - How? 

Comment voyage-t-elle aux Etats-Unis? - How is she going to travel to the U.S.?

Pourquoi? - Why? 

Pourquoi est-ce qu’il pleure? - Why is he crying?

Combien? - How much? 

Combien coûte-t-il? - How much does it cost?

Combien de? - How many? 

Combien d’enfants avez-vous? - How many children do you have?

Que? / Qu'est-ce que? = What? (as the subject) 

Que as-tu fait? / Qu'est-ce que tu as fait? - What have you done?

Quel (m.sing.)/Quels (m.pl.)/Quelle (f.sing.)/Quelle (f.pl.) + noun - What? Which? 

Note that quel agrees in gender and number with the noun that follows it. 

e.g.

Quel docteur? - What/which doctor? 

Quelle voiture? - What/which car?

Qui? / Qui est-ce qui? - Who? 

Qui a dit cela? / Qui est-ce qui a dit cela? - Who said that?

Qui? / Qui est-ce que? - Whom 

Qui as-tu vu? / Qui est-ce que tu as vu? - Whom did you see?

All of these interrogative adverbs can be used to ask questions with either est-ce que or inversion.

   Quand manges-tu ? Quand est-ce que tu manges ?

   When do you eat?

   Combien de livres veut-il ? Combien de livres est-ce qu'il veut ?

   How many books does he want?

   Où habite-t-elle ? Où est-ce qu'elle habite ?

   Where does she live?

They can be used in indirect questions:

   Dis-moi quand tu manges.

   Tell me when you eat.

   Je ne sais pas combien de livres il veut.

   I don't know how many books he wants.

   J'ai oublié où elle habite.

   I've forgotten where she lives.

Comment, où, and quand can also be used with n'importe.

   Tu peux manger n'importe quand.

   You can eat whenever / any time.

In literature or other formal French, you might see an additional interrogative adverb: que, meaning "why":

   Qu'avais-tu besoin de lui en parler ?

   Why did you have to go and talk to him about it?

   Olivier et Roland, que n'êtes-vous ici ? (Victor Hugo)

   Olivier and Roland, why aren't you here?

Source

http://www.learn-french-help.com/french-interrogatives.html

https://www.thoughtco.com/french-interrogative-adverbs-1368800?_ga=2.182284576.643170086.1496816867-1700346625.1468207072