The purpose of a volt-ohmmeter is to check:

A volt-ohmmeter is an essential diagnostic tool in electrical work, specifically designed to measure resistance, as denoted by the "ohm" in its name. When using this device, technicians can determine how much opposition there is in a circuit or component, which is crucial for troubleshooting electrical systems.

Resistance measurements, indicated in ohms, are key in evaluating whether components are functioning correctly or if there might be a short circuit or open circuit in the system. While this tool also has the capacity to measure voltage, its primary utility lies in its ability to assess resistive properties effectively.

In the context of the other options provided, frequency, capacitance, and power are not parameters measured by a volt-ohmmeter, thereby reinforcing that resistance is indeed the primary focus of this specific instrument.