Group Policy involves 2 replications type. AD Replication and SYSVOL replication
AD Replication can be verified by using the repadmin command
repadmin /showrepl
repadmin /replsummary
SYSVOL replication can be verified in the EventLogs (Applications and services logs / DFS Replication)
You can also use the dfsrdiag command if there is a backlog
RGName = Replication Group Name --> By default it's "Domain System Volume"
RFName = Replicated Folder Name --> By default it's "SYSVOL Share"
smem = Sending member --> DC1
rmem = Receiving member --> DC2
dfsrdiag backlog /RGName:"Domain System Volume" /RFName:"SYSVOL Share" /smem:DC1 /rmem:DC2
run the same command by changing source / destination
ref:
hth