You don't need an Analysis Workspace project in order to query data using the Analytics API. The Analytics API allows you to query any data the API caller (either an authenticated user via oAuth or a service token via JWT) has permissions to view, regardless of whether that data is displayed in a Workspace project.
If you want to query the same data that is displayed in a Workspace project, you can use the Workspace debugger to see how Workspace formulates the API requests. Using the Workspace debugger to see how to formulate report requests is a hand technique that's documented here: analytics-2.0-apis/reporting-tricks.md at master · AdobeDocs/analytics-2.0-apis · GitHub