It possible you dont have one...without listener.ora, a listener will just assume all of the defaults. If one is there, it should appear in a STATUS command, eg
LSNRCTL> status
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=localhost)(PORT=1521)))
STATUS of the LISTENER
------------------------
Alias LISTENER
Version TNSLSNR for 64-bit Windows: Version 12.1.0.2.0 - Production
Start Date 16-JAN-2017 07:50:10
Uptime 4 days 12 hr. 26 min. 35 sec
Trace Level off
Security ON: Local OS Authentication
SNMP OFF
Listener Parameter File c:\oracle\product\12.1.0.2\network\admin\listener.ora
Listener Log File c:\oracle\diag\tnslsnr\COMCDONA-AU\listener\alert\log.xml