Can i fit a turbo on a stock peugeot 206cc 1.6 16v engine and how much power will i gain?

Gray area is correct.

Making extra power will also stress the transmission more.

Peugeot make the cars as light as possible so do not build in extra strength in case

Breaking transmission bits is expensive.

The car will be worth less with a turbo. Insurance will go up and many companies will not even quote for the car.

Many who will quote will need you to pay for an engineers report.

You can slap a turbo on most anything. How much power you will gain depends on many factors like turbo size, pipe length, intercooled or non intercooled, how much boost the turbo will run and on and on. Another factor is how short will the engine life be because it was not designed to handle boost from the factory.

You would be better off selling the car and buying a different car that already has a turbo from the factory. You clearly do not have the mechanical skill set or knowledge to install a turbo which would make the cost of paying for the installation prohibitive.