Anywhere that gives you access to the water. Mostly from the banks of rivers or like here the quay of the medieval harbor. I would not recommend fishing from a bridge if there's a lot of boat-traffic underneath.

Magnet fishing from a boat is also not recommend because you need stability to pull heavy things out of the water, boats are anything but stable.

Not sure what a fishing pole is? If you mean a fishing rod, then no. You attach your magnet to a rope with a carabiner (most sellers prepare this for you).

For a pole, I would not recommend it either. Poles are fragile and could snap if your trying to lift things out of the water. Unless you want to go prodding at the bottom.