If you're looking for the actual January Jumble riddle, you can find it here! Are you absolutely, positively sure that you want to see the answer now? If you haven't even tried to solve it, go back to the question! It's not that hard :)
FOR THE MOMENT YOU'VE ALL BEEN WAITING FOR....!
The solution to this problem is quite simple once you've gotten to know how to word your question properly.
The most straightforward solution is to ask one of the two people, "Would you tell me if your path leads to the Amusement Park?"
If the Knight was standing in front of the path to the park, it would tell you that the path behind him was the path to the Amusement Park. Something even better is that the Knight would tell you that it would tell you that the path leads to the Amusement Park, as it always tells the truth. (that sentence was a weird one!)
However, if the Knave was standing before the path to the Amusement Park and you asked him if it was the right path, it would lie and say no. But if you ask the Knave if it would tell you that the path led to the amusement park, it would lie and say yes. The Knave is saying that it would tell you the truth about the path, which most definitely, is a lie.
Here's the summary: In both cases, if you asked one of the people, "Would you tell me if your path leads to the Amusement Park?", both of them would answer yes if it did lead to the right destination regardless of whether they were a Knight or a Knave. Similarly, if the path led to certain doom and you asked if they would tell you if their path led to the Amusement Park, they would both say no.
A more technical way of solving this problem would be using a Truth Table and listing out all the possible outcomes. Have a try yourself!