Either "VRM" under the ASUS EC sensor (if present) or "VR VCC" under the CPU sensor (if present). But I'm not sure if that model features a VRM that can measure and report temperature.
What kind of precaution? I'm new to all this stuff and this rig has to last me for about 5 years. So I'm just wondering what kind of precaution are we talking about?
It is described in the warning you got - reading that sensor might cause higher latency or stability issues on some systems. But this is a rare effect.