Teradata SQL Assistant - List tables under DBC in the Database Explorer
By default, Teradata SQL Assistant will attempt to query the views DBC.Databses, DBC.Tables, DBC.Columns to populate the Database Explorer. It is possible in your environment that those objects are not accessible to developers or end users via the PUBLIC user. Instead, you may need to modify your connection settings ODBC or .Net Provider to use the X-Views in DBC. These are a collection of views which restrict the rows returned based on the privileges your user account has been granted to access or which you have created.

The ODBC DSN, .Net Provider, and JDBC drivers for Teradata have a means to use the X-Views by default to enable database tools such as SQL Assistant or Teradata Studio/Studio Express to populate the database explorer controls "transparently". Try this and see if it works.