An Infrared Thermometer prefers a non-reflective surface to accurately read the temperature reliably - glass is reflective for Infrared light under many angles and can in the worst case result in measuring anything but what you want to measure. To that degree, a piece of paper tape (Painter's tape or Washi-tape works fine) can act as a mounted measuring point.
A contact temperature sensor can be mounted touching the plate in a location easily by putting it in contact using some tape.
However, do note that the temperature sensor of the printer is not mounted on the top of the build platform but at the heater element under it. This means two things:
There is a temperature differential between the heater (which would be quite hot but not scorching in an instant of touching it) under the aluminium bed, the top of the aluminium bed, and even more if correlated against the surface of your build platform.
On the other hand, to verify your sensor setting, you need to measure under the bed at the heating element or at the interface between the heater and the aluminium bed. For example, you could use a spot right next to the heater as your probing point. This is incidentally quite close to where the temperature sensor should be mounted anyway.
Bed temperature control
Depending on your setup, the temperature difference between heater and the build surface could be up to about 15 °C and I would deem that an acceptable number. In accounting for the wanted build surface temperature, one can adjust the set heater temperature accordingly, as shown in this experience I had:
On particularly a cold day in late 2021 the heating in the room was not gaining enough heating water from the central unit set to a lower setting than it ought to. As a result, the room was down from the usual temperature to a rather cold ca. 12 °C. On that day I had to increase the bed temperature by a couple of degrees to gain proper bed adhesion, but it fixed itself once I figured out to fix the setting on the central unit.