Answer:
(2, 2)
Explanation:
Plotting the points, it should be obvious where the fourth corner needs to be: (2, 2).
_____
When the sides of the square are parallel to the axes, as here, each x-coordinate will appear twice, as will each y-coordinate. The ones in the list of given points that appear only once are x=2, y=2, so those are the coordinates of the missing point.
___
The two points that make up a diagonal of the square are (0, 2) and (2, 0). The missing point is the sum of these less the remaining point:
(0, 2) + (2, 0) - (0, 0) = (2, 2)
This is because the midpoints of the diagonals are the same point, hence the sums of endpoints of the diagonals are the same.