'VOLT,AGE'

'VOLT','AGE'

SQL> select regexp_replace('AB,CD','(..),',q'['\1',]') from dual;
'AB',CD

SQL>select regexp_replace('AB,CD,DE','(..),',q'['\1',]') from dual;
'AB','CD',DE

SQL> with data as (select q'['VOLT,AGE']' v from dual)
  2  select v, replace(v, ',', q'[',']') v2 from data;
V          V2
---------- ------------------------------
'VOLT,AGE' 'VOLT','AGE'

WITH data AS 
  (SELECT q'['VOLT,AGE']' v FROM DUAL)
SELECT v,
       REPLACE (v, ',', q'[',']')              v2,
       REGEXP_REPLACE (v, '(.),', q'[\1',']') r1
  FROM data;

v               v2               r1
----------------------------------------------
'VOLT,AGE'	'VOLT','AGE'	'VOLT','AGE'

with data as (select q'['VOLT,AGE']' v from dual)
select v, replace(v, ',', ''',''') v2 from data;

V          V2
---------- ------------------------------
'VOLT,AGE' 'VOLT','AGE'