Is an carnival an proper or common noun?

No, the compound noun 'amusement park' is a common noun, a general Word for any amusement park.

A proper noun is the name of a specific person, place, or thing. A proper noun for the common noun amusement park is the name of a specific amusement park; for example, Disneyland in Anaheim CA or Dollywood in Pigeon Forge, TN.