Do I need to any airport transit visa?
For Amsterdam? Assuming that you're arriving at and departing from Schipol you do not need a visa for the Netherlands since you will not be entering the country, just the transit area of the airport.
You'll basically get off the plane, follow the signs for the transit area and (assuming you're checked in right the way through to Gdańsk) go at your leisure to the gate for the Gdańsk flight. If you aren't checked in, you'll need to go to the transit desk for a boarding pass; this is increasingly rare. Usually better to check-in online if possible.
You will of course need a visa when you go through immigration at Gdańsk.
I'm assuming by the way that it's a proper layover, and that you're booked (and your luggage checked in) all the way to Gdańsk. Rather than a flight to Schiphol and a seperately booked ticket on a low cost airline like Ryanair/Wizzair to Gdańsk.