I have an app... how do I make it so that any comment on a part of the activity produces a push notificatioin to the owner of the original activity?

Can I use Auto action for that? I have found under system activity the mention "push comment"... no idea what that does though...

I am aware that we can use our own code for push notification, I just need to know if that is the right trigger/if it only notifies the person whose post has been commented on OR if it notifies everyone who has commented on this post AND the original owner of the post.

If you want to log an activity entry every time someone comments on an activity entry then enable the system action "CB Activity - Comment" (you will need CB Auto Actions 6.3.1). Who can see these entries is entirely based off the stream being viewed. For example the recent activity page will show it to everyone. The profile activity page will show only activity you made or that your connections made.