You can configure the listener with logging and tracing parameters.
Log information is typically stored in the listener.log
file located in $ORACLE_HOME/network/log
on UNIX and ORACLE_HOME\network\log
on Windows platforms.
Trace information is stored by default in listener.trc, located in $ORACLE_HOME/network/trace on UNIX and ORACLE_HOME\network\trace on Windows platforms.
To enable logging or tracing:
In the navigator pane, expand Oracle Net Configuration > Local > Listeners.
Select a listener.
From the list in the right pane, select General Parameters.
Select the Logging & Tracing tab.
Adjust the logging and tracing settings as needed.
Choose File > Save Network Configuration.