"What kind of salespersons are you looking for?"
Translation:Te milyen eladókat keresel?
Milyen acts like an adjective here, since it's not the predicate.
Milyen eladók? = What salespeople?
Milyenek az eladók? = What are the salespeople like?
Compare: this two phrases: "magas eladók" vs "magasak az eladók."