I want to control TOS5300 series by a programmable logic controller (PLC). Can I connect the COM (circuit common) terminal of the TOS5300’s SIGNAL I/O connector to the COM terminal of the PLC’s +24 V internal power supply terminal?

Yes, you can.
However, the COM terminal of TOS5300’s SIGNAL I/O connector is the common terminal for both its input and output signal terminals, which is internally connected to its LOW VOLTAGE terminal.
Therefore, it is at the ground potential.