If you don't need a fancy function that detects exactly where you press, but just that you press, then you can implement three resonance circuits and check the frequency of the circuits. It is quite similar to metal detectors and different proximity sensors. But what is the reason that you require a glass plate? That you need to display information through the glass, or because you need your equipment behind a show window, or just because you consider a thick glass plate to be scratch and break resistant for something similar to a bank teller machine?

But as already shown, capacitive sensors are affected by electromagnetic fields so it is important that you are reasonably in control of the environment for the installation and that a false trig doesn't activate potentially dangerous operations.