how to test transistor side of optocoupler using multimeter?

 

Generally, you can't unless the transistor has the base connection available externally.
What is the optocoupler?
Does your multimeter have a transistor test option?

 

If the base pin is there then it should check like a normal transistor on the Diode check scale.
Max.

 

Even if the base pin isn't there, you could try connecting the + and - probes of a DMM to the collector and emitter pins respectively, setting the DMM to an Ohms range, passing a small current through the opto LED and looking for a change in the meter reading.

 

Put your meter on Diode test, across the C/E of the opto, power up the led and it should read or beep.

 

Thank you all.
The optocoupler do not have the base pin. So I need to use second method you mentioned.