Listener.ora Location
You will find listener.ora in here: 


  %ORACLE_HOME%/network/admin


The usual problem is that %ORACLE_HOME% isn't set as a system variable and not exposed to a command shell. 

My quickest way to locate ORACLE_HOME from the command shell is:

C:\&gt;where sqlplus
The full path to the executable will show. Go there.
Go one up, and add /network/admin


Another approach is to look in the registry.

Watch out for variable TNS_ADMIN which overrides Oracle default network directory.