If something is the smokiest, it has the most smoke or smells like smoke the most.
The word smokiest can make people think of a lot of smoke, maybe from a fire or from cooking.
Examples:
The smokiest room in the house is the kitchen.
The campfire was the smokiest I've ever seen.
The smokiest part of the city is near the factories.
The smokiest chimney in town is on Mrs. Smith's house.
After the fire, the whole forest was the smokiest place ever.
The smokiest barbeque in the world is at the park near my house.