Not being Catholic myself, I will certainly admit that my perceptions may be in error. However, my perceptions are based on the following:
Vatican II (Lumen Gentium 25)
Vatican II explained the doctrine of infallibility as follows: “Although the individual bishops do not enjoy the prerogative of infallibility, they can nevertheless proclaim Christ’s doctrine infallibly....
Catechism 882
The Pope, Bishop of Rome and Peter’s successor, “is the perpetual and visible source and foundation of the unity both of the bishops and of the whole company of the faithful. For the Roman Pontiff, by reason of his office as Vicar of Christ, and as pastor of the entire Church has full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered.”
Based on these (and other writings) it appears to me that Papal supremacy is the doctrine of the Roman Catholic Church. Further, that the pope, by reason of his office as Vicar of Christ and as pastor of the entire Christian Church, has full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered. This would include the power of interpretation of scripture and dominion over canon law.
The point of my question is to call out that when Popes are wrong, what other than scripture, would a Catholic use to even measure that the Pope is wrong. This then goes to support prima scriptura.
Based on these (and other writings) it appears to me that Papal supremacy is the doctrine of the Roman Catholic Church.
Absolutely, but please keep in mind that this is not the same as saying that every theological opinion he holds must be the one all people hold. He is as capable of being wrong as anyone, on a personal level, and that means that well informed and sincere Catholics can, and sometimes must, disagree with him. Supremacy is a juridical issue, and does not confer on the Pope personal impeccability and constant infallibility.
This would include the power of interpretation of scripture and dominion over canon law.
Yes, to a point. But, a pope cannot contradict the faith of the Church, which existed before him and will exist after him. He is only empowered by God to protect what he has received, not to change it or recreate it. If a Pope rejects the historic Catholic faith he has moved outside of the faith. The faith does not move along with him. He is just wrong in that instance.
The point of my question is to call out that when Popes are wrong, what other than scripture, would a Catholic use to even measure that the Pope is wrong. This then goes to support prima scriptura.
No, not at all. A Catholic must measure everything they see and hear, regardless of where it comes from, by comparing it to the Catholic faith, which naturally includes scripture as that is a crucial part of the Tradition of the Church. But, ultimately, we are called to look at the entire history of the Church and all that she has pronounced, not just the most recent comments. That is the problem with so much we see and hear today. It is all about looking at the Church as only being governed and informed by one Church Council, and the most recent popes. Not so at all. As a matter of fact, real Catholic faith rests in seeing and hearing all of these recent events and teachings as being limited and constrained by all that came before and has been believed from the beginning. Without that we would be no different than any reformed church which moves with the whims of their leaders. Popes are Catholic not because they define Catholicism, but because they are defined by it.