The question is on the your of your law.
John 8:17 says:
It is also written in your law, that the testimony of two men is true.
In this case, the law is from Deuteronomy 17:6, which says:
At the mouth of two witnesses, or three witnesses, shall he that is worthy of death be put to death; but at the mouth of one witness he shall not be put to death.
Jesus was not implying that this law wasn't also Jesus's law. Had he done so, or had the Pharisees even suspected that he was implying this, they would have jumped on that attitude as blasphemous. But they didn't.
The Pharisees were morality police. They not only expected everyone to follow the letter of the law, they expected everyone to go far beyond the letter, so that there couldn't be the slightest doubt that the letter was being followed. To them, nothing was more important than the Law.
Jesus was simply using a rhetorical device, employing the Pharisee's own weapons against them. The Law was their most precious thing, so by making an explicit reference to their law, Jesus made it difficult for them to disagree with him.