It is not as simple as just a number or value. You have 3 outputs coming out of the stator all at the same time that are 120 degrees out of phase with each other. You also have RPM injected into the equation and on top of that would you like an RMS or Peak value. If RMS, you would have to use a True RMS meter because the value you read will depend on the RPM of the engine. Then there is the question of wanting the values loaded and by how much. If loaded, what load value are you going to use. If your using the regulator in the bike, what if one of the regulator outputs happen to be shorted, then what. The value you read will be near zero and your going to think the stator is bad when it isn't. To really make any sense of what you see, you will need a scope to view the sine wave.
To truly test the stator you would have to "Ring" the 3 coils in the absence of the rotor. That will tell you if you have a shorted turn. Remember, only the crests of the waveforms charge the battery, not the bulk of the waveform itself. How will you measure that?
There is no simple magic number you can just read. If there was, the service manual would go into it.
Maybe someone else has the number your looking for but I don't see anything that is practical other than the ohm meter & smell test.