Network Latency
During a DA session, it is not possible to get the latency between clients, due to how the network topology works - handling networking through a service broker - there are no packets sent directly to other clients that could be used to measure network latency.

You can get the Round Trip Time (RTT) between the local client and the broker using GetCurrentRtt
NetworkManager.Singleton.NetworkConfig.NetworkTransport.GetCurrentRtt(NetworkManager.ServerClientId)
Ping Times
The Netcode for GameObjects Ping Tool has been built for example purposes to showcase how to acquire ping times between clients during a network session for both Client-Server and Distributed Authority topologies.
As this is an example project, it could have bugs or areas that could be improved, therefore it is recommended to be used as a reference, with customization required to integrate into your project depending on your own needs and goals.