125 kHz RFID Antenna Measurement using CRO - Passive Probe
On RFID resonant circuits the Q is not usually so high that you can't place 100kohm in parallel with it. That's the first point. The second point is that the 100k could be 99k and 1k in series with the 1k connected to ground. Connect your scope across the 1kohm to do measurements.

The 1kohm and 100pF of your probe won't start to attenuate frequencies till about the 3dB point and that is: -

\$\dfrac{1}{2\pi\cdot RC} = \$ 1.6 MHz.

OK there will be attenuation of 100:1 but it may be visible. If it isn't I'd consider using a decent fast op-amp stage as a gain of ten to help out your viewing of the signal.