function OnMouseDown()
{
var pos : Vector3 = transform.position;
Debug.Log(pos);
}
Transform.Translate does not return a value- it should be used to move a transform, not to query its position.
Of course, this script only works on one object at a time- to get the position of a clicked object in a more general way, you would use Camera.ScreenPointToRay and Physics.Raycast.