Hi, for those interested, after several attempts I was able to find the working command line for cronjob that works with websites hosted by Siteground. Here the example:

/usr/bin/wget --spider "http://yoursitename.com/index.php?page=cron"
Return reply (is an example that I have recived in email from my server alert):

Spider mode enabled. Check if remote file exists.
--2021-07-27 15:00:01--  http://yoursitename.com/index.php?page=cron
Resolving yoursitename.com (yoursitename.com)... 35.214.185.39
Connecting to yoursitename.com (yoursitename.com)|35.214.185.39|:80... connected.
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://yoursitename.com/index.php?page=cron [following]
Spider mode enabled. Check if remote file exists.
--2021-07-27 15:00:01--  https://yoursitename.com/index.php?page=cron
Connecting to yoursitename.com (yoursitename.com)|35.214.185.39|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Remote file exists and could contain further links,
but recursion is disabled -- not retrieving.

Thanks for your guide, very appreciated