There's no single answer to the average horsepower of a car because it varies wildly depending on the type of car, its age, and the country where it's sold. A small, fuel-efficient city car will have significantly less horsepower than a large pickup truck or a sports car.
While you can find statistics on average horsepower for specific car segments (like sedans or SUVs) in particular regions and years, a global average would be meaningless due to the vast differences.