Did Jesus witness her adultery?
No
The fact you think the Pharisees weren't breaking the Law proves you don't actually know the Law.
They didn't think they were breaking the law. Tradition had compromised some laws, but other than that they were strict law keepers.
There is the letter of the law, which the pharisees followed, and the spirit of the law which exposes the sin nature. However, as long as they didn't commit the act of sin by breaking the law, they were free of outward external condemnation.
Jesus came to expose the heart, and to show that although people may not commit the act of sin, the desire to to commit sin exposes the inner man.
Romans 7:5 For when we were in the flesh, the sinful passions which were aroused by the law were at work in our members to bear fruit to death.
You see that?
Sinful passions are aroused by the law, which is why Paul said, "that which was supposed to bring life, actually brought death.
Why?
Because God originally created Adam and Eve to have dominion. The flesh was not created to serve anything or anyone. Therefore when it comes under legal restraint, the inner desire is to rebel. Jesus came to expose that inner desire (sin nature), in the hope that people would respond as Paul did......
But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members. O wretched man that I am! Who will deliver me from this body of death?