Is it possible in some way find out for which notifications is subscribed some user, query or some other way?
I gave idea earlier for that functionality in PI System Explorer, Management.
AFNotificationRuleSearch supports the ContactName and Contact search filters starting from AF 2017. You can use these to perform the search
is it possible to do through a query, without programming?
Notification Contacts Export
Check this thread; query at the end - modify as needed.
I've used this to do exactly what you are asking for.
Retrieving data ...