Following query can be used to get list of all TFS email alert subscriptions.
List of subscriptions is maintained in tbl_EventSubscription table of each collection database.
Use following query to find list of subscriptions. (Replace Tfs_TFSSupport by required project collection database name).
SELECT [Id]
,[EventType]
,[Expression]
,[SubscriberId]
,[Schedule]
,[DeliveryType]
,[Address]
,[Classification]
FROM [Tfs_TFSSupport].[dbo].[tbl_EventSubscription]