er det korrekt correct ?

"favorittrestaurant" skrives som ett ord, ikke to. (This is written as one word, not two. However, a lot of Norwegians make mistakes in this area, mainly because of the influence of English, which doesn't string several words together in the same manner as the other Germanic languages.)

As you see I use duolingo and there are some interesting exercises like this one. but there is no correction.
My level is very low so I can't express more than some basics a little basis, and, overall I don't go to the restaurant so often! 

I know that sometimes we put the possessive pronoun before the noun, and other times after. Could you help me with these different uses? 

I've noticed that learners struggle with this, but I don't know if there's a rule. I just hear what sounds better. So maybe it's just one of those things you pick up as you learn the language for a while and get enough exposure to it. Your sentence is not wrong, but I would rather write "i favorittrestauranten min".

(you can also correct the English part of this entry if you want! I think it would be more efficient to write in English than in French but I am possibly wrong).

Et si quelqu'un qui passe sur ce post souhaite apprendre le français je peux aider !

French is on my list, maybe next year :)