Instantiate a Prefab along the surface of a sphere. C#

That's pretty vague. How do you want to place it there? How is the sphere created? Do you want it to be random?

     public Vector2 PlaceAlongCircle() {
         Vector2 circleCenter = new Vector2(14f, 32.3f);
         float radius = 5f;
 
         Vector2 rand = Random.insideUnitCircle * radius;
         return circleCenter + rand;
     }

I haven't tested this but i think it would work. http://docs.unity3d.com/ScriptReference/Random-insideUnitCircle.html