In case somebody might need this in future, I finally found the controller.
components/com_community/controllers/system.php
These functions were used
public function ajaxStreamAdd($message, $attachment)
- goes into jom_community_activities table where$message
is the text entered in the "Share" box and$attachment
is a JSON-encoded string that contains the target, actor, access-level, app etcpublic function ajaxStreamAddComment($actid, $comment)
- goes into jom_community_wall table where $actid is the userid of the user posting the $comment
Best Regards