Translation:Are they cooking for me?
It will depend on the noun class of the object .e.g. onion (kitunguu, noun class 'Ki/Vi') as an indirect object would be: 'Wanani
As a direct object, it depends on whether you're speaking generally or referring to a specific onion ('a/an' versus 'the'):
Are they cooking an onion for me? - Wananipikia kitunguu?
Are they cooking the onion for me? - Wanani