How to locate currently used listener.ora file?

e.g.
Find oracle client which is using by server:
$ which sqlplus
-- /ora11g/orahome/bin/sqlplus

Check listener.ora:
$ cat /ora11g/orahome/network/admin/listener.ora
-- e.g. port -> 1521

Ref: https://ozsoyler.blogspot.com/2016/11/how-to-configure-listener-port-when-it.html