You can access to the diagram tables and browse through their objects by mean of the Object Tree View, that represent all the diagram objects, including tables, in a tree-like structure.
To expand table, click on the "+" sign near the table name, it will show you table columns and indexes. Click on the "-" sign to roll up the list.
Examine the following table-related features in the Object Tree View:
Interface User Guide: Docking Windows
Diagram Objects: Column Editor | Table Editor | Index Editor