AGLatency is a tool to analyze AG log block movement latency between replicas and create report accordingly.

You can download version 2.2 here: https://github.com/suyouquan/AGLatency/releases/download/V2.2/AGLatencyV2.2.zip

Video: https://github.com/suyouquan/AGLatency/blob/master/AGLatency_HowTo.mp4

Manual:
https://github.com/suyouquan/AGLatency/blob/master/AGLatencyTool_UserManual_V2.pdf

You capture log block Xevent trace from both primary and secondary replica for 5-10 minutes and then this tool will generate report about the latency of the log block movement.

Reference link:
https://blogs.msdn.microsoft.com/psssql/2018/04/05/troubleshooting-data-movement-latency-between-synchronous-commit-always-on-availability-groups/

New in SSMS – Always On Availability Group Latency Reports https://blogs.msdn.microsoft.com/sql_server_team/new-in-ssms-always-on-availability-group-latency-reports/

select
AGNode.group_name
,AGNode.replica_server_name
,AGNode.node_name,ReplicaState.role,ReplicaState.role_desc
,ReplicaState.is_local
,DatabaseState.database_id
,db_name(DatabaseState.database_id) as database_name
,DatabaseState.group_database_id
,DatabaseState.is_commit_participant
,DatabaseState.is_primary_replica
,DatabaseState.synchronization_state_desc
,DatabaseState.synchronization_health_desc
,ClusterState.group_id
,ReplicaState.replica_id
from sys.dm_hadr_availability_replica_cluster_nodes AGNode
join sys.dm_hadr_availability_replica_cluster_states ClusterState
on AGNode.replica_server_name = ClusterState.replica_server_name
join sys.dm_hadr_availability_replica_states ReplicaState
on ReplicaState.replica_id = ClusterState.replica_id
join sys.dm_hadr_database_replica_states DatabaseState
on ReplicaState.replica_id=DatabaseState.replica_id
for XML RAW, ROOT('AGInfoRoot')

Note: Please copy only the xml data to the result file, like below primary.xml:

--You can change "c:\temp" to other folder accordingly.

CREATE EVENT SESSION [AlwaysOn_Data_Movement_Tracing] ON SERVER
ADD EVENT sqlserver.hadr_apply_log_block,
ADD EVENT sqlserver.hadr_capture_filestream_wait,
ADD EVENT sqlserver.hadr_capture_log_block,
ADD EVENT sqlserver.hadr_capture_vlfheader,
ADD EVENT sqlserver.hadr_db_commit_mgr_harden,
ADD EVENT sqlserver.hadr_log_block_compression,
ADD EVENT sqlserver.hadr_log_block_decompression,
ADD EVENT sqlserver.hadr_log_block_group_commit ,
ADD EVENT sqlserver.hadr_log_block_send_complete,
ADD EVENT sqlserver.hadr_lsn_send_complete,
ADD EVENT sqlserver.hadr_receive_harden_lsn_message,
ADD EVENT sqlserver.hadr_send_harden_lsn_message,
ADD EVENT sqlserver.hadr_database_flow_control_action,
ADD EVENT sqlserver.hadr_transport_flow_control_action,
ADD EVENT ucs.ucs_connection_flow_control,
ADD EVENT sqlserver.hadr_transport_receive_log_block_message,
ADD EVENT sqlserver.log_block_pushed_to_logpool,
ADD EVENT sqlserver.log_flush_complete ,
ADD EVENT sqlserver.recovery_unit_harden_log_timestamps
ADD TARGET package0.event_file(SET filename=N'c:\temp\AlwaysOn_Data_Movement_Tracing.xel',max_file_size=(500),max_rollover_files=(4))
WITH (MAX_MEMORY=4096 KB,EVENT_RETENTION_MODE=ALLOW_SINGLE_EVENT_LOSS,MAX_DISPATCH_LATENCY=30 SECONDS,MAX_EVENT_SIZE=0 KB,
MEMORY_PARTITION_MODE=NONE,TRACK_CAUSALITY=OFF,STARTUP_STATE=ON)
GO

--Now start it and keep it running for 10 minutes

ALTER EVENT SESSION [AlwaysOn_Data_Movement_Tracing] ON SERVER STATE=START;

/*
--You can stop it this way:

ALTER EVENT SESSION [AlwaysOn_Data_Movement_Tracing] ON SERVER STATE=STOP;

*/

Put AlwaysOn_Data_Movement_Tracing.xel and primary.xml from primary to a folder, say, c:\data\primary, and put AlwaysOn_Data_Movement_Tracing.xel from secondary and secondary.xml to another folder, say, c:\data\secondary. And then feed the tool with these two folders, click "Start" to generate the report.

Note: Your SQL server may need to be updated to support above xevents:
https://support.microsoft.com/en-us/help/3173156/update-adds-alwayson-extended-events-and-performance-counters-in-sql-s