Question

Why do we get dew on the surface of a cold soft drinking bottle kept in open air?

Answer 1

There is a different in temps from the bottle to the air. Its condensation . The more colder the water or drink is the more condensation on the bottle of a hot day . COLD WATER+HOT WATER = More condensation.  

Answer 2

We see small drops of water on the bottle of a cold soft drink water kept in air because the air surrounding the bottle, when comes in contact with the cool surface of water condenses to form water, and this water is seen as drops on the bottle.