I have recently got a mac an am not used to developing on a mac at all.
I have MAMP Pro 18.104.22.168. I did a locate on
$ locate php.ini
/Library/Application Support/appsolute/MAMP PRO/conf/php.ini
Note: If this doesn't help, check below for Ricardo Martins' answer.
Create a PHP script with
<?php phpinfo() ?> in it, run that from your browser, and look for the value
Loaded Configuration File. This tells you which
php.ini file PHP is using in the context of the web server.