What skill can be learned in a week that can make most people go "Wow!"?
Can it be the Rubik's cube or what else?
Rubik's cube. You can get algorithms off the web and practice them for a week and get good enough to solve the cube within 5-10 minutes.
The thing about the Rubik's cube is that there is a point where it looks like you are undoing what you did. But then it suddenly comes together. What happens in the last layer is that you usually find pairs of moves. Baically let's say you have the 4 edge pieces in the wrong place. You group them into 2 pairs that can be flipped to get them in the right spot. You flip the first pair without worrying about any of the layers under the layer being fixed. Then you flip the second pair, but this time you flip them in the reverse direction.
To a person who doesn;t know what you are doing, it looks like you are messing up the cube, but when you get to flipping in the reverse direction, all the layers below your layer automatically get back to where you started (since you are basically reversing your moves). It looks like you did the whole cube in a couple of moves.