I learned today that there is a Project Server 2013 reporting database schema tool that can be downloaded. Here’s the link to more information and the download itself: http://blogs.msdn.com/b/project_programmability/archive/2013/01/28/project-server-2013-reporting-database-rdb-schema-reference.aspx. There are differences in reporting of on-premises vs. Project Online. For Project Online, you can use REST queries of the ProjectData OData service. See the links for info.
The Project Server 2013 reporting schema includes three new tables, 27 new views, and a total of 33 tables and views that include new fields.
For those invested in reporting, this is your field day!