which is correct quelle luxe or quel luxe

cq. 

Without a lesson/exercise link, this looks, rightly or wrongly, like possible homework. 

Internet search is your friend - the following 2 links will help you to the answer and the reason.

Quel/quelle/quels/quelles + [nom] = What a [noun] (French Exclamative Adjectives) 

https://www.wordreference.com/fren/luxe