Find out the user and its privileges in Oracle

Check all user having administrative privileges

select * from V$PWFILE_USERS;


Check all system privileges granted related to all users/roles.

SELECT * FROM DBA_SYS_PRIVS;

GRANTEE is the name, role, or user that was assigned the privilege.
PRIVILEGE is the privilege that is assigned.
ADMIN_OPTION indicates if the granted privilege also includes the ADMIN option.
 
Check object level privileges to User

select * from DBA_TAB_PRIVS;

GRANTEE is the name of the user with granted access.
TABLE_NAME is the name of the object (table, index, sequence, etc).
PRIVILEGE is the privilege assigned to the GRANTEE for the associated object.
 
Check all the roles granted to users/roles

select * from dba_role_privs;

 
Check all the column level privileges for user/role

SELECT GRANTEE, TABLE_NAME, COLUMN_NAME, PRIVILEGE FROM DBA_COL_PRIVS;

 
Find out current user permissions

-- your permissions
select * from USER_ROLE_PRIVS where USERNAME = USER;
select * from USER_TAB_PRIVS where GRANTEE = USER;
select * from USER_SYS_PRIVS where USERNAME = USER;