Identifying roles on a projects
To generate a report listing all roles that have been assigned to a project, do the following:
If you assigned roles to tasks on a project, then you can use the report source Project/Task report source All Task Roles on a Project.
If you did not assign resources to project tasks (the resources don't have task roles or tasks schedules), then you'll have to use the Business Unit/Project report source All Project Roles on All Projects in a Business Unit