There isn't a specific term for the act of measuring a liquid's temperature and observing it boil. It's just a combination of two processes:

* Measuring the temperature: This is done with a thermometer.

* Observing the liquid boil: This refers to the process of a liquid changing into a gas due to heat.

The term you might be looking for is "determining the boiling point", which is the specific temperature at which a liquid boils under a given pressure.