What is a WSAPI query to get all users of my subscription?
To receive all users of your subscription user the a query against the User endpoint.
https://rally1.rallydev.com/slm/webservice/v2.0/user?query=(SubscriptionID = "<Your Subscription ID>")&fetch=true&start=1&pagesize=20
You can refine your results by modifying the 'fetch' , 'order' and 'pagesize' values.
The result of this query will the complete collection of your subscription users. You can use the 'TotalResultCount' returned field to learn of the total number of users.
Note: This query returns all your subscription users, including all disabled and all locked users.