"We are reading the restaurant's menu."
Translation:Ni legas la menuon de la restoracio.
Is "Ni legas menuon de la restoracio" acceptable, if I'd be reading a "whatever menu" of some exact restaurant?
If you were to say that in a real-life Esperanto sentence, it would sound completely natural and I would know exactly what you were talking about, so I'd say yes. The meaning is a tiny bit different, though - the menu is somehow related to a restaurant, but it might belong be "the" restaurant you were talking about earlier.