"He does not know anything but classical genres."
Translation:Nezná nic kromě klasických žánrů.
They are transgressives - a grammatical form of verbs not very much used in the spoken language.
But some transgressives became fixed expressions used not strictly accordingly according to the rules of transgressives but more like prepositions. And "vyjma" (less often "vyjímaje" or "vyjímajíc") is one of these.