user which holds objects grants DBMS_METADATA.GET_GRANTED_DDL

The user hold any object grants.

which will generate you a list of DBMS_METADATA.GET_GRANTED_DDL statements for every user which holds objects grants .....

set pagesize 100
set linesize 200
set long 5000
select 'select DBMS_METADATA.GET_GRANTED_DDL(''OBJECT_GRANT'','||''''||a.username||''''||') from dual;'
from dba_users a, (select distinct(grantee) from dba_tab_privs) b
where a.username = b.grantee
/

then run the script