Turbocharged
 

What kind of endorsement on ppl sep need to fly turbocharged single piston?

Welcome Grofvon, I can't speak to specific licensing, though I doubt that turbo alone would require its own endorsement. More likely that the aircraft by its configuration requires an endorsement, perhaps RG or other more advanced characteristic.

Most turbo systems are pretty straight forward to operate, just keep an eye on the manifold pressure to assure that the maximum is not being exceeded. A few planes are manual, and thus the pilot must carefully set, and thereafter monitor and reset, the throttle so as to not exceed the manifold pressure limit. Such aircraft can be easily overboosted and the engine damaged if you open the throttle too much.

Croatia is a beautiful country to fly!

I think we need more information. What licencing regime are you under?