(a) Electrical field is normal to the surface at two points only
This is true. The direction of electric field coincides along the line joining the two charges. Hence at points A and B where the line joining the two charges meet the sphere, we have electrical field normal to the surface. This is possible only at points A and B of surface of sphere and nowhere else.
(b) Electrical field is zero at no point.
This is true. Since magnitude of charge is same , electrical field will never vanish due to both the charges on the surface of sphere.
(c)Electric potential is zero at every point of one circle only.
This is true. Electric potential is scalar quantity and function of distance from test point to charge. As shown in figure, it is possible to find points lying on a circel which are equidistant from the two charges. Since distances are same and sign of the charges different, potential vanishes. In figure only two points C and D are seen which are satisfying this condition. Since the figure shows cross section of sphere, we see only two points C and D, but if you consider the surface of entire sphere, we get a circle where the points are equi-distant from both the charges, hence potential vanishes at every point along this circle only
(d) all of the above :- true