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 /