Currently you can only view obsolete data entities in the data entities page in the Data Management workspace. (System administration > Workspaces > Data Management > Data entities tile> filter for obsolete).

It would be incredibly useful to see what data entities are obsolete in all data projects, rather than drilling down to each individual data project. This could be implemented on the Data projects > All projects table as a column to add to be able to filter and see what data projects are affected.