What would be the Catholic response to someone such as Geza Vermes who claims that others besides Jesus (Hanina Ben Dosa, for example) were also called the “Son of God” and were also known to work miracles?
First and foremost, one asks such people to substantiate their claims. They should be encouraged to do so from primary sources from history, not from tracts, booklets, or other such secondary materials that simply reiterate their claims. Once you have their sources you can check the sources themselves for context.
Simply the title “Son of God” and an ability to work miracles does not mean that a person is equivalent to Christ’s unique claim to be the Son of God. Catholics acknowledge, for example, that all baptized Christians are considered sons and daughters of God by adoption. What your inquirers must prove is that the usage of the term “Son of God” by others means that they should be regarded in the same manner as God the Son. As for miracles, if they are good they must be credited first to God and not to the person through whom God, for whatever reason, chose to allow them to occur.