How Do We Know What “Most Scholars” Think?

I have received a particularly interesting question that has led to a bit of back and forth between me and a person on the blog. This person pointed out that in my writings I often indicate that a view that I have (e.g., that the Gospel of John was not written by John the son of Zebedee; that the book of Ephesians was not really written by Paul even though the author claims to be Paul; or that the Gospels are all 40-65 years after the death of Jesus, etc.) is held by the majority of scholars....