In order to know which printer specifically is out of paper you would need to copy the "Out of Paper Errors" component and specify the printer in the instance field pictured below, and repeat this process for each printer you would like monitored.
A simpler method might be to use the Component Monitor Wizard, located under [Settings > SAM Settings] and browse the "Print Queue" Windows Performance Counter category, selecting each printer you want monitored in the "Out of Paper Errors" counter, as pictured below.
