How to measure the impedance of a given coil?
I don't know what kind of equipment you have exactly but if you have a function generator that can output a decent sine signal at 13.56 MHz you should be able to use that in conjunction with an oscilloscope to get a reasonable measurement of the inductance. Be aware that proper probing techniques at these kind of frequencies are necessary in order to get a usable result. This interesting article by Tektronix explains the process quite clearly: https://www.tek.com/document/application-note/capacitance-and-inductance-measurements-using-oscilloscope-and-function-ge