"Nānā!"

Translation: Look!

[Filip_Prague]

Why isn't it "E nana", if it is an order?

[Maui_Bartlett]

While you can certainly say "E nānā!", and that is an accepted answer for this exercise, it is often shortened in casual speech to just "Nānā!" This can happen with other words as well (usually single words or short phrases), but "nānā" is shown this way here because it is one that is commonly heard.