Session variables can be found in gv$ses_optimizer_env. Use this query to find the values set for a particular user or session:
select o.name,
o.value,
s.logon_time,
s.prev_exec_start,
s.status,
s.sid,
s.inst_id,
s.username
from gv$ses_optimizer_env o,
gv$session s
where o.inst_id = s.inst_id
AND o.sid = s.sid
and s.username = 'APPLICATION USER'
order by s.logon_time desc
/