The line of the gravitational force pass through the center of the earth but there is also a centrifugal force on the body at the surface due to rotation of the earth. If the direction of the centrifugal force is different from the gravitational force, the line of action of the net resultant force will not pass through the center of the earth. And this is the case at places other than the poles or equator. 

(a) At the equator:- 

The centrifugal force due to the rotation of the earth is vertically upward. This results in a reduction in the magnitude of the net force but the line of action passes through the center of the earth. So the normal to the free surface of the liquid will pass through the center of the earth.  

(b) At the poles:- 

The magnitude of the centrifugal force due to rotation of the earth is zero because the radius of the rotating circle is zero. So there is no change in the magnitude and the direction of the gravitational force here. Therefore the normal to the free surface will pass through the center of the earth.  

(c) Somewhere else:- 

As stated in the beginning, the net force on a body will not pass through the center of the earth anywhere else, the plumb-line will also not pass through the center of the earth. Since the horizontal line or the free surface of a still liquid is perpendicular to the plumb line So the normal to the free surface of the liquid will not pass through the center of the earth.