“My ex-wife received full custody of our son while she resided in the State of Wyoming. My son has been incompetent from birth and is now 30 years old. Both she and my son live together now in Florida. If I want visitation with my son, what must I do and in what State must this be done?”
Generally under the Uniform Child Custody Jurisdiction and Enforcement Act (UCCJEA), the Court that originally issued orders concerning child custody would retain jurisdiction to make further orders. That would be the Court in Wyoming. Since nobody lives in Wyoming, a transfer of venue to Florida may be indicated. As near as I can gleen (and you are advised to seek counsel) you likely would need to ask the Court to appoint a guardian ad litem for your son to help decide whether visitation with your son is indicated.
Before hiring a Wyoming attorney to change venue to Florida (or even your home state), try talking to your -ex about whether you can spend time with your son.