Is it at all possible to say Han er restaurantens kokken?
That would be like saying "He is the restaurant's the cook." in English. (It would not be possible)
Why does it sound like she's saying 'restaurangens'?
I also hear "restaurangens"
My boyfriend said thay it's wrong pronunciation (he is Norwegian)
It's actually correct.
"Restaurant" is a French loan word, and that's why "ant" is pronounced as "ang".
From my understanding depending on where you live in Norway you either pronounce it French style or English style.
What is wrong with saying "Han er kok til restauranten"
Should be fine if you spell kokk correctly.