The grants are stored in view that have the privs suffix (Privileges).
select * from all_objects where object_name like '%PRIV%';
The most important is the table (dba|user)_tab_privs. It shows the privileges of the following type:
Example:
select * from table_privileges;
SELECT
owner,
table_name,
PRIVILEGE
FROM
dba_role_privs rp
INNER JOIN role_tab_privs rtp ON (rp.granted_role = rtp.role);