In the first part (Mark 2:1–12) he shows this by doing something that only God can do, which is forgiving sins. In the sequel he makes statements (in Mark 2:17, Mark 2:19) in which he says things about himself that an ordinary person can never fulfill, for example, in Mark 2:17 he calls sinners to repentance and calls himself the bridegroom.
1 And when he returned to Capernaum after some days, it was reported that he was at home.