How to wire the output of a PLC
No, you won't see any voltage between COM and O1. According to Omron's web page there are several different variants of this PLC. Some have relay outputs and others have transistor outputs. Either way, you need to provide AC or DC (in the case of relay) or just DC (in the case of transistor outputs). This is shown in your diagram by the AC voltage sources and dotted battery symbols. You need to check which version you have (see page 6 of the datasheet for the output configurations).

If you have a relay model, try connecting a multimeter set to a resistance range between one of the 'O' terminals and it's COM terminal.