Where is the castle?

Relevant wiki: Truth-Tellers and Liars

Alex says "Dont listen to Jim" (states that Jim never speaks the truth). Jeff says "Listen to Jim" (states that Jim always tell the truth). These statements are contrary to each other, so either of them must be true.

If Jim was the knight (always honest), Jeff would also tell something true. However, there is only one knight, and the others are knaves ( who always lie ), so Jeff and Jim can't both tell the truth, so Jeff's statement (Jim is honest) is false.

This means Alex must have told the truth, and because he is the knight (and always tells the truth) his first statement is true, and the castle is in the north.

Just assume any one of them is knight and follow and then again for rechecking assume another ad knight till we can sure

Since all four people give different statements on the first answer, we must decide their truthfulness based on their second answer. Jim says to listen to Jeff, who in the first statement gave a different answer than him, so he was lying at least in one of his two statements, but since Knaves always lie and Knights never lie, it means that he lied on both statements. Same goes for Jeff. Since we know that Jim and Jeff are Knaves, and since Alex says not to listen to Jim, he's truthful; while Alice says not to listen to Alex, therefore to listen to Jim, who is a Knave. So the only one speaking the truth is Alex, and the right answer is North.