How much horsepower will be added?

I have a 2006 ford f150 harley davidson edition and a supercharger was put in it from previous owner, about how much horsepower and torque should it have with the supercharger?

Also don't forget to search this on Google.

Superchargers can vary in how much boost they give out. This means they could add anything from 10 to 300+ hp. It all depends on how it is set up. Usually for the extreme builds you'd need other performance parts to match the performance of the supercharger. You'd need a performance exhaust, intake, fuel systems, cooling and other parts. One of the main things about superchargers is that while they don't give as much max RPM horsepower as a turbo, they drastically improve low RPM torque. This means that a supercharger might not increase HP by a lot but it will still make the truck a lot faster.
Personally, I would bet that the supercharger gave that truck around 50 hp and a lot more low end torque. Maybe around 75 or 100 lb ft. I would also guess that the peak of torque would be lower giving you a much wider power band to work with.

It's going to depend on the supercharger volume and how fast you spin it. You really need a chassis dynomometer to run it and get accurate numbers.

It would depend on the type and size of the supercharger, aswell as depend on other upgrades that have been done to the engine. I mean if he put towing mirrors on it, those are good for 20 horse each. The only way to find out for sure would be to find a tuner and use a Dino to give you the numbers.