Is he considered either a king or a great non-Jewish scholar?
As an absolute monarch, he has the capacity to exert control over the military (if he desires) and is technically capable of enacting capital punishments in accordance with Canon Law (Catholic Halacha). We may liken this with the President of the United States who has the power to execute or commute capital punishment, for whom one says the berachah for seeing a king, according to R' Ovadia Yosef זצ”ל (see above linked answer).
You said correctly that one makes a blessing on a king and on a great non-Jewish scholar.
A king is a head of state. The Poskim debate if one recites this blessing on a president or prime-minister. The blessing is definitely not recited on a powerful person who is not a head of state.
A great non-Jewish scholar is defined as one who has exceptional knowledge in one of the sciences. See Blessings on Wise Men and Kings.
The pope does not meet either condition. There is no blessing for a respected religious leader of a (non-Jewish) religion.