Q:

how to select a Oracle schema-specific view from another schema

Suppose I'm logged in as USERA, I want to access all the user_* views of the USERB schema, such as user_tables, user_tab_columns. How can I do this? Thanks

A:

All the USER_* tables have analogues with the ALL_* and DBA_* prefix.  USER_TABLES has information about all the tables you own.  ALL_TABLES has information about all the tables you have access to.  DBA_TABLES has information about all the tables in your database.
If you want to see information about UserB's tables
SELECT *
  FROM all_tables
 WHERE owner = 'USERB';

or 
SELECT *
  FROM dba_tables
 WHERE owner = 'USERB';

The former will work if you have SELECT access on User B's tables.  The latter will work if your DBA has given you access to the DBA_TABLES view.  That is normally done by granting the SELECT ANY DICTIONARY privilege (or the SELECT_CATALOG_ROLE in prior version) though the DBA can grant access to individual DBA_* views.

