Security is at the gate in PRG, so I'm pretty sure you'll arrive into the main terminal (what I mean by this is that on arrival you’ll find yourself in the departures area, which is used by arriving and departing passengers, and contains shops and restaurants, as well as access to the gates and to the exit).

There will be no immigration as you're non-Schengen to non-Schengen and then you'll have security at the gate.