How can the actual cabin temperature be observed?

Observing the actual cabin temperature can be accurately done by reading the temperature displayed on ED2. The Electronic Display 2 (ED2) provides real-time data that reflects the current conditions within the cabin, including temperature, which is crucial for ensuring passenger comfort and aircraft performance. This information is obtained directly from the aircraft's environmental control system, making it the most reliable source for cabin temperature readings.

The other options might provide information relevant to the cabin environment but do not directly display the current temperature. For instance, the cabin pressure indicator gives insights into pressure levels, while the ambient temperature gauge measures external conditions rather than the internal cabin temperature. Monitoring air conditioning settings offers context on how the temperature is being controlled, but it does not provide an actual temperature reading. Therefore, ED2 serves as the most effective means to observe and confirm the cabin temperature.