Against jax, Jax’s Ultimate t will give him increased defensive stats in a trade. It is very good for duelling.

Once Jax gets his first item, he becomes much harder to duel unless you have items that match his damage. Don't over commit to fighting him without a backup plan.

As the game goes along, Jax will get stronger and stronger. Keep an eye on him at all times as he will look to split push and take objectives quickly.  Against jax, It is very good for the duelling. Once Jax gets his first element, it becomes much more difficult to duel unless you have elements that match his damage. Do not commit too much to fight him without a backup plan. As the game unfolds, Jax will become stronger and stronger. Keep an eye on him at any time he will seek to divide the thrust and take goals quickly.