I want to post a story but I’m not sure if people will know I posted it. To be clear, if I put a photo or video on my Instagram story, will it show me a list of everyone who has viewed it, and will those people know that I can see they watched it?
Instagram stories do show a list of viewers, but only to the account that posted the story. Viewers will not know who else has watched it unless they also view the list themselves. If you want to analyze viewer data privately, consider using a third-party service like DFViewer.
Oh, I always worry about this too! 
So, if you post a photo or video on your Instagram story, yes, you will be able to see a list of everyone who viewed it. Instagram shows you exactly who watched your story.
And yes, the people who view your story don’t get a notification that you can see them, but if they know how Instagram works, they might realize that you can see their name in your viewers list. It’s not a secret, but Instagram doesn’t send them an alert or anything.
Are you planning to post something private? 
Just to be sure—are you okay with knowing exactly who saw your story, since you’ll have that info? And is it okay with you that your viewers might realize you can see them? Let me know if you want tips on keeping your stories more private!