You can get all the details about your Drush installation by running:
* Drush 8
$drush status --fields=drush-conf,drush-script,drush-version,drush-temp, drush-alias-files
Drush configuration : /etc/drush/drushrc.php
Drush script : /usr/local/drush8/vendor/drush/drush/drush.php
Drush version : 8.4.2
Drush temp directory : /mnt/tmp/xxxx
Drush alias files : /mnt/drush/xxxxx/xxxxx.aliases.drushrc.php
* Drush 9
drush status --fields=drush-conf,drush-script,drush-version,drush-temp,drush-alias-files
Drush configs : /etc/drush/drush.yml
/mnt/www/html/xxxxx/docroot/vendor/drush/drush/drush.yml
Drush script : /mnt/www/html/xxxxx/docroot/vendor/drush/drush/drush
Drush version : 9.7.2
Drush temp : /mnt/tmp/xxxxx
Drush aliases : /mnt/drush/xxxxx/xxxxx.site.yml
When you want to override the Drush alias with a new file , you can easily find the path for the new file.