What we know about the term Son of Man is that it wasn’t used as a term with a messianic title in Jewish literature. It was only until when the Gospels were written that it has taken on the meaning of a messianic title. The term Son of Man in this the Jewish literature context had two roles, revealer and messenger of the “eschatological break in time.” An example would be in Daniel 7:13-14 the passage talks about Daniel seeing something that was “One like a human being coming with the clouds of heaven”. The context of the sentence “One like a human being” would be referring to an angel, who most say was the angel Michael, who was the guardian of Israel. The angel came to be a revealer in Daniel’s dreams.
At the end of 1 Enoch, Enoch reveals that the Son of Man is himself. After researching a bit about who Enoch is, I learned that he is known as the great-grandfather of Noah. Since Noah is a descendent of Adam, this would mean that Enoch would have been a direct descendent from Adam. This plays a great role in world history because it has importance on the family line that descends from Adam all the way down to Jesus. Enoch wouldn’t be important to Jews in the context of history if Enoch wasn’t related to the bloodline of Adam. In 1 Enoch it is possible that Enoch was saying that you have to be a ‘son of man’ in order to be included the blessed line of Adam.
If I were a Jew living in the first century, I think my response to the readings in Mark would be a couple of things, suspicious, confused and I would question myself and also Jesus. Mainly because my perception of whom the Son of Man is would not be in the form of an actual man and more in the form of an angel who looks like a man. After reading Mk 8:31, I would remember the apocalyptic references like in Daniel and Enoch but I would be confused and skeptical of why the Son of Man would be the one that is going to suffer if my understanding of the Son of Man is solely a revealer and messenger. The non-believers or people who were not righteous were the ones who were supposed to be suffering.
At the same time, I wouldn’t be so quick to dismiss that Jesus could be the Son of Man that was written in earlier literature. The reason would be that Jesus quotes passages from Daniel multiple times and ties it in to the destruction that he tells the disciples what is going to happen and it in fact actually does happen. In Mk 14:53-62 Jesus is brought to court with the high priest and all the chief priests, the elders and the scribes and they ask him if he is the Messiah, the Son of the Blessed One. He responds proclaiming that he is the Messiah then quotes again a part of the passage from Daniel mentioning that we will see the Son of Man coming with the clouds of heaven.
In summary, I think it would be hard to not be interested of who this Jesus figure is and what he claims to be. I am not sure if I would disagree with what Jesus was proclaiming but I don’t think as a first century Jew I would be quick to jump on board with what he was asking us to believe either.