The Church is all Catholics. Catholics are baptized, confess the true faith in word and deed, and submit to their authorized superiors. Since there are no bishops with apostolic mandate left, there's none to submit to.
This. Non-sedevacantists like to say "Is SSPV or whoever the Catholic Church?" The question is silly and makes no sense. The Catholic Church is the congregation of all those who are baptized, profess the Catholic Faith, and are submitted to its legitimate authority. Traditional Catholic organizations such as SSPV do not claim that only people who attend their chapels are Catholic. And the question "Where is the Catholic Church" is like asking "Where is the Pythagorean Theorem?" The Catholic Church isn't sitting in a box somewhere. It's a spiritual thing that does not exist in a place, so it's meaningless to ask for its location.