In Catan (seafarers), there is a new piece introduced: the pirate ship. When you move the pirate ship, even without a knight card, you get to take a resource from the owner of an adjacent boat. If you use a knight, would you get two resources, one for moving the pirate, one for the knight, or would you just get one? It doesn't really say in the book as far as I'm aware, and the wording doesn't seem to hint at it in either way.
No, the pirate ship acts in the same way that the robber does, allowing you to steal 1 resource.
Playing a Knight card by itself does not allow you to steal a resource from a player. Playing a Knight card allows you to move the robber, and if you place the robber next to a player, then you get to steal a resource from that player. The pirate works exactly the same, placing the pirate next to a player allows you to steal a resource from the player.
From the Seafarer rules:
- If you roll a "7" during your turn, you may elect to move the pirate INSTEAD of the robber. Like the robber, you place the pirate in the center of any hex you choose--except that you may only place it on a sea hex. You are then allowed to steal one random resource from any ONE player who has a ship adjacent to that hex! If a player has more than one ship adjacent to that sea hex, you are only allowed to steal one card from that player.
- If you play a knight card, you now have the choice of moving either the robber or the pirate.
And from the base game rules:
If you play a knight card, you must immediately move the robber. See "Rolling a '7' and Activating the Robber" above and follow steps 1 and 2.
So the Knight card by itself does not allow you to steal a resource, it is only the robber, or the pirate in the case of Seafarers, that allows you to do so.