In order to get the datastore name that is experiencing the high latency you would need to use the "Datastore High Latency" alert vs using the "Host to Datastore Latency" alert. The reason you are probably having trouble corresponding the alert to a specific datastore or VM with high latency is that the Host to Datastore Latency alert actually provides an aggregate of all latency for the host. In contrast when you choose the Datastore High Latency alert you get the datastore experiencing the high latency and you can modify the email alert to display the datastore name by selecting insert variable, change show variable to Virtual Datastore and select Name from the list of variables. This will display the name of the datastore with high latency in the body of the email.
I already also have that alert enabled and set to email, but it was set for the condition to exist for 15 mins as my other one had no time on it. I changed it to no time so I will see next time I should get an alert from both I would think.
The "Datastore High Latency" alert also looks to be a total though, but slightly different.
Alert on Virtual Datastore --> Latency Total -- is greater than or equal to 20.
"Host to Datastore Latency"
Alert on Virtual Host --> Total Latency --> is greater than 20.