It depends on the resonant frequency of the the crystal and the properties of the amplifier inside the processor. What the processor, a digital device, will "see" is a signal with two states and short transitions between the stares at a periodic rate. There is not much else to say about the waveform that could be considered useful.So if we dont connect any probe, since it effects the meausrement and distort the signal by loading.
What exactly is shape of signal at XTIN & XTOUT of MCU when a crystal is connected acrss it with each pin having capacitor to GND?
Is it sine, square, distorted sine?