Question: What is the form of the soul?
Answer: Well, this is a quite advanced question but I will try to make it simpler.
See, originally the soul has a spiritual form. And that form is based on the relationship with the Supreme Soul, what will be the activity, the service and so on between the soul and the Supreme Soul. But in the material world the soul loses his spiritual form if you will because he is no longer in the position.
So we are described as like a spark, the spiritual spark. So the form that we know in the material form is the form of the bodies, and according to our relationship with the world we have different forms which change each lifetime on the wheel of birth and death.
So these are the material forms of this world but when we again reestablish this loving relationship with God and we return to the spiritual world according to that relationship, we will have a spiritual form.