Does the author of Mark knows that Jesus was the son of God?
The third century Gospel of Mark does not have the words "The son of God". Unfortunately, the scribes of the Gospel of Mark have allowed themselves to manipulate the Biblical text as they wished.
Codex Sinaiticus, a third century Bible. 1:1 The beginning of the gospel of Jesus Christ,
2 As it is written in Isaiah the prophet: Behold, I send my messenger before thy face, who shall prepare thy way:
Mark 1:1 NIV. 1 The beginning of the good news about Jesus the Messiah, the Son of God,
2 as it is written in Isaiah the prophet: “I will send my messenger ahead of you, who will prepare your way” —
Codex Sinaiticus link is https://codexsinaiticus.org