Well, in most cases, if the Instagram user has not set any restrictions on their story sharing, you are allowed to share it. But keep in mind that some people might not like their stories being shared without permission even if the settings allow it, so it's always polite to ask first. Also, if there are any copyright or intellectual property issues involved, that could be a problem too.
Yes, they can. Instagram provides some analytics and notifications that may indicate when someone has shared their story. For example, if the person has a business account or uses certain insights tools, they might be able to see that their story has been shared.
Sorry, you can't. Instagram doesn't provide that kind of notification. But some third-party apps claim to do it, but they might not be reliable or violate Instagram's terms of use.
As of now, Instagram doesn't notify you when someone takes a screenshot of your story. So, no, you can't really know if someone has screenshot your Ig story.
As of now, unfortunately, Instagram doesn't give any indication about who has screenshot your story. It's a bit of a bummer for those who might be concerned about their content being screenshot without permission. But it also means that users can share and view stories more freely without the worry of being tracked for screenshotting.