Thank you Jansay for your answers !

However, I don´t agree with your second point.

With certain words such as "Neden, Nasıl, Hangi..." we never use -mi. For instance :

Neden bunu yaptın ? = Why did you do that ?

Dün ne yaptın = What did you do yesterday ?

In those cases we don´t need -mi so why does in this case we use it ?

2) We simply can not form a question without "-mi". There´s just a tiny exception with words like "Tamam" "Oldu" where we can just say them like we´re asking questions without having to add -mi; but otherwise -mi is mandatory.

Niçin?

Ne?

Ne zaman?

Nedir?

Nerelesin?

Kaç?

(Just teasing you J.) 

O haha matdamon said the same 

I see Matt´s point, this question Ne mi göruyorum ? already has Ne. So I´m wondering how it is different from Ne göruyorum ?

According to this page: https://www.facebook.com/290576441016020/posts/450330761663665 adding mi to something that is already a question is to show surprise or even annoyance.

I was just about to correct that statement. You people are so harsh! =P

Oh right, now I remember: -mi is used there to emphasize on "ne". We use it like that too sometimes. It´s all about the syntax; check out these two sentences:

Bakkala gittin mi? (Did you go to the store?)

Bakkala mı gittin??? (Did you go to the STORE?) (Showing surprise)

Hope it was helpful,

-Jansay

Thank you everyone,

It´s crystal clear now