Well, generally, Instagram shows the list of people who watched a story to the person who posted it. However, there are some privacy settings and workarounds. For example, if you view the story anonymously using third - party apps (which might violate Instagram's terms), the person may not be able to tell it's you. But if you use the normal Instagram app to watch, they can find out. Also, if they have a large number of viewers, they might not notice that you specifically watched their story, but the information is there for them to see if they look.
Most likely, yes. The viewer list on Instagram for a story doesn't distinguish between single and multiple views in a very obvious way. So if you watch a story again, your name is still there in the list of viewers. However, the person who posted the story might not notice if they have a large number of viewers. But technically, they have the means to see that you've watched it more than once if they look closely at the list.
As of now, Instagram doesn't notify the story owner when you screenshot their story. It's one of those things that Instagram has decided not to implement for privacy reasons perhaps. But this has been a topic of debate among users. Some think it should be notified for privacy and content ownership reasons, while others like the freedom it gives to users to save content for personal use without the creator knowing.
I'm not sure. Maybe you could check your account settings or see if there's a notification related to it. Or you could try to remember if you had any specific actions that indicated you watched the story.