M2E Pro uses its own Cron Service that manages the synchronization process. Please, read more about data communication via the M2E Pro server and why the automatic synchronization is required.
However, if you want to set up Magento Cron to run M2E Pro Cron tasks, you should follow the instructions below.
Command PHP: php -q /%PATH_MAGENTO_ROOT_CATALOG%/cron.php -mdefault 1
Command GET: GET http://%YOUR_DOMAIN%/cron.php
crontab -u -e
* * * * * /bin/magento cron:run
It is strongly recommended to set up Cron to run every 1 minute (e.g. * * * * *). Please check this post (true for all versions).
If automatic synchronization still doesn't work, read this article for the solution.