Hi,
Every user can query the ALL_XXX views such as ALL_TABLES, ALL_VIEWS, ALL_OBJECTS etc..
These views provide for all objects that user has privileges too.
You can query the DBA_TAB_PRIVS to view all user table privileges:
select owner,table_name,privilege,grantee
from DBA_TAB_PRIVS
where owner not in ('SYS','SYSTEM');

cheers
R.