How to measure trace impedance?
There is no* way to measure trace impedance with a simple multimeter.

Measuring trace impedance requires, at minimum, an oscilloscope and an impulse generator of some sort. Here's an article about how you can measure the impedance of a cable (or PCB) with a signal generator.

Doing "Proper" impedance measurements requires a special tool, called a network analyzer.

* No reasonable way, in any event. There may be ways to abuse a specific model of meter in a specific manner to get a approximate result, but it won't be generalizable.