There is currently no way to query for data in closed projects via the Web Services API (WS API). If you know the ObjectID of a closed project you can directly read it, but that's the only way.
For example: https://rally1.rallydev.com/slm/webservice/v2.0/project/170646754824
The only way to retrieve work item information from closed projects via WS API is to re-open the closed project temporarily, obtain the needed reporting, and then close them. WS API queries are scoped to open projects only to optimize performance.
Another option is to leverage the Lookback API to query on a snapshot of data. Learn more about LBAPI at https://rally1.rallydev.com/analytics/doc/#/manual
Learn more about closed projects at https://communities.ca.com/thread/241789993-what-are-closed-projects