Smart City Layers are curated data for your Smart World projects. You are free to use the data in any way you wish- they are included with your Smart World license!
To see what Smart City Layers are available in your area of interest just zoom to your area (any level works) and click the Smart City Layer button in the left hand side menu bar.
From that list, just double click any layer to add it to an Asq query. Once the query has populated, just hit enter and the layer will load.
At this point it is treated as any Asq Query. You can modify it, save it, or delete it as you would any other query.