the replication between Datastore servers. Replication is managed by Cloud Bigtable and Megastore, the underlying technologies for Datastore
Replication for Cloud Bigtable enables you to increase the availability and durability of your data by copying it across multiple regions or multiple zones within the same region
How can I see in the datastore UI if I'm getting any replication? If I am getting replication how can I see if I'm getting cross region or cross zone replication for my datastore entities?
(The entities I'm looking at have been populated since 2017 if that's useful.)
The short answer to your question, is that if you are in a multi-region then you can already access your data from multiple regions without worrying about asynchronous replication lag.
If you are really curious about Megastore replication, you can read the Megastore paper. However, what's more likely that you want is to read the trade-offs between strong consistency & eventual consistency in Datastore.
The locations for Cloud Datastore currently match those of Cloud Firestore in either mode.