It will depend how you are controlling the VFD Drive
PD050 may do what you want, depending on your VFD Drive model it may be 04 some are using 03 and or 04 for Zero speed you may also look at PD052 as you could use these relays also
You won't measure anything, the For and DCM are just switched with a Relay normally
DRV is an opto output you need a +24v / 100ma voltage to use these outputs ( Which can be supplied by the drive if it has a +24v )