Where is my wpa_supplicant.conf?

Solution 1:

If you use NetworkManager to configure your wifi connections look in /etc/NetworkManager/system-connections

There should be files in there for all your configured network connections.

Solution 2:

wpa_supplicant doesn't run with a conf. It's a daemon that communicates with your network manager using DBUS. You can see what's happening with wpa_cli which will show you the instructions being received by the daemon.

That's not to say you can not run with a configuration file, you can. But, Ubuntu doesn't use that configuration file at all. It's all remotely controlled through the DBUS api.