Does my son's father have a right to an accounting of my sons trust now after his Death.

If your son's father is a beneficiary under the terms of the trust (someone who will receive property from the trust upon your son's death) he would be entitled to an accounting.  He would also be entitled to an accountng if he is to become a successor trustee of the trust.  He could also be entitled to an accounting if a minor or disabled beneficiary of the trust is served by him as a guardian or conservator.  He is entitled to notice of the existence of the trust because he could be in "intestate heir," but that alone would not entitle him to an accounting.