Please, read my comment to the solution 1 by Kornfeld Eliyahu Peter.
I'm almost sure it's impossible to get time zone name in Oracle server, because it's not supported.
I believe you need to write
custom function[
^]. The basic idea is to get time offset and compare it with the list of time zones, than to return proper time zone name.
Have a look here:
A Time Zones[
^]
Obtaining Time Zone Names[
^]
Note: i don't have access to Oracle database/server, so i can be wrong.
BTW: It might be useful too:
Converting Time Zones With the AT TIME ZONE Clause[
^]