If I understand correctly: for input [1, 3, 5, 9] and 2, you understand that result should be -1 (because 2 is not in the array), and kata expects 25 (because value 5 is at index 2). Do I get the problem right?

You should find the N-th power of the element in the array with the index N

Not a kata issue.

Currently, your solution passes without problems. Can you show what code and what inputs cause problems for you?