For suppose if I want sysdate,
SELECT SYSDATE as system_date FROM DUAL;
should output in the following format
14-Feb-2018 T19:50:02+00:00
i.e.,
DD-MMM-YYYY Thh:mm:ss+HH:MM
Assuming you know the date represents UTC and want the +00:00 part to be fixed:
select to_char(sysdate, 'DD-Mon-YYYY "T"HH24:MI:SS"+00:00"') from dual;
TO_CHAR(SYSDATE,'DD-MON-YYYY"T"HH24:
------------------------------------
14-Feb-2018 T20:13:08+00:00
The format model elements are in the documentation. That includes a section on character literals, which I've used for the fixed T and +00:00 parts.
As @mathguy said, this seems a bit unusual; and you might actually to leave the column as a native date and have your application or reporting tool or whatever format it for you. It depends what exactly you're doing, and whether you actually want a string value directly from the query.
As your updated question now doesn't have that pseudo-timezone, it's now even simpler, but the same idea:
select to_char(sysdate, 'DD-Mon-YYYY "T"HH24:MI:SS') from dual;
TO_CHAR(SYSDATE,'DD-MON-YYYY"T
------------------------------
14-Feb-2018 T20:17:50
If you're working with a data type that knows about time zones - i.e. not a plain DATE or TIMESTAMP - you can include those in the formatting using the appropriate model elements:
select to_char(systimestamp, 'DD-Mon-YYYY "T"HH24:MI:SSTZH:TZM') from dual;
TO_CHAR(SYSTIMESTAMP,'DD-MON-YYYY"T"
------------------------------------
14-Feb-2018 T20:24:58+00:00
which happens to still show +00:00 because my system is in the UK. With a different value it shows something appropriate:
alter session set time_zone = 'AMERICA/NEW_YORK';
select to_char(current_timestamp, 'DD-Mon-YYYY "T"HH24:MI:SSTZH:TZM') from dual;
TO_CHAR(CURRENT_TIMESTAMP,'DD-MON-YY
------------------------------------
14-Feb-2018 T15:28:57-05:00
Notice now I'm using systimestamp and current_timestamp, which are TZ-aware, and not sysdate or current_date which are not - you'l get an error if you try to get the TZH or TZM elements from those.