In every world so far, Hint Toad has put a star on these green robots. However, they only seem to let you look around. How do you get a star from them?
After beating the game, each kingdom is populated with many new elements. One such element is that several kingdoms have flying airships from the Cap Kingdom cruising around high in the sky. In several instances, one of the airships will be a unique object -- a sphynx or a taxi instead of the normal hat-shaped flying machine. If you take control of the green binoculars and zoom in on that unique flier, a moon will appear for you to collect.
Grabbing that moon will complete the objective the Hint Toad is indicating.