I know where you are coming from, but there has to be some sort of limit, right? I mean, if a bishop observes a national public figure who condones and facilitates Satanism at every opportunity (and publicly proclaims Satanism is perfectly compatible with Church teaching) in the Communion line but whose base of operations isn’t in his diocese, what should he do?
Freegards
He cannot do anything, officially. But if the person in question comes to that very bishop to receive communion, he may refuse him, as ANY priest may, if he’s certain it would be a sacrilege to give him the sacrament. That’s a separate issue from the bishop’s role. But in terms of pastoral or disciplinary measures, every single Catholic in the world has a bishop and is subject to that bishop, whether or not they recognize it. In the situation you’re describing, the bishop has no authority, but he certainly could in confidence communicate with his brother bishop who has the jurisdiction over the person in question and let him know what he observed.