If you wan to know the sync status of a always On availability group database replication, this command can be used:

SELECT 
	ar.replica_server_name, 
	adc.database_name, 
	ag.name AS ag_name, 
	drs.is_local, 
	drs.is_primary_replica, 
	drs.synchronization_state_desc, 
	drs.is_commit_participant, 
	drs.synchronization_health_desc, 
	drs.recovery_lsn, 
	drs.truncation_lsn, 
	drs.last_sent_lsn, 
	drs.last_sent_time, 
	drs.last_received_lsn, 
	drs.last_received_time, 
	drs.last_hardened_lsn, 
	drs.last_hardened_time, 
	drs.last_redone_lsn, 
	drs.last_redone_time, 
	drs.log_send_queue_size, 
	drs.log_send_rate, 
	drs.redo_queue_size, 
	drs.redo_rate, 
	drs.filestream_send_rate, 
	drs.end_of_log_lsn, 
	drs.last_commit_lsn, 
	drs.last_commit_time
FROM sys.dm_hadr_database_replica_states AS drs
INNER JOIN sys.availability_databases_cluster AS adc 
	ON drs.group_id = adc.group_id AND 
	drs.group_database_id = adc.group_database_id
INNER JOIN sys.availability_groups AS ag
	ON ag.group_id = drs.group_id
INNER JOIN sys.availability_replicas AS ar 
	ON drs.group_id = ar.group_id AND 
	drs.replica_id = ar.replica_id
ORDER BY 
	ag.name, 
	ar.replica_server_name, 
	adc.database_name;