phyin,
In order to measure the charge of an electron you need some fairly complicated laboratory equipment. Here is an example from George Mason University:
"In this experiment we will measure a fundamental property of the electron, the ratio of
its charge to its mass.
In the experiment, a beam of electrons accelerated by a potential difference is bent into
a circular path by a magnetic field. The beam is in a glass container containing a small
amount of gas of a fluorescent molecule. Some of the electrons in the beam collide with
these molecules, and this results in the emission of light. This process produces a visible track corresponding to the electron beam, so the radius of curvature of the electrons may be measured by eye. By also measuring the accelerating voltage of the electrons, and the strength of the magnetic field the electron's charge to mass ratio is determined.”
See: physics.gmu.edu/~ellswort/p263/eoverm.pdf