College Physics (4th Edition)

There are no points not on the x-axis such that $E = 0$.
If a point is not on the x-axis, then the y-component of the the electric field due to each point charge will be non-zero and point in the same direction. Therefore, the y-component of the net electric field will be non-zero. There are no points not on the x-axis such that $E = 0$.