Migrated a DC and wanted to do some basic AD health checks.
From the cmd prompt (domain joined pc with sufficient privileges or on the DC):
repadmin /replsummary repadmin /showrepl
Query FSMO role holders, which should confirm that they are online:
netdom query fsmo
General Server Diagnosis:
dcdiag /a /s:<DC server name>
If you want the DC's to force sync and see if there are any issues: