Question

Measure the reactance of an inductor

Answer 1

You need to know the voltage and current, then you can calculate the reactance.

With a dual trace oscilloscope, you can do this. Set channel A to measure the voltage across the component.

You can measure the current using the 'scope, but it takes a little more thought. You'll need a resistor of very low resistance. Something 1/20th the expected reactance of the component you are testing and non-inductive. A metal film 0.1 ohm resistor in series with the inductor or capacitor, between ground and the component, will give you 100mV per ampere or 1mV per 10mA of current.

You don't need to worry about calculating RMS current or voltage. Ohm's law holds for RMS or peak, as long as you use the same all through.