Of course. To unblock someone on Snapchat that you had blocked from your Snap Story, start by opening the Snapchat app. Then, access the settings. Scroll through until you find the list of blocked users. Identify the person you wish to unblock and take the necessary steps to unblock them. However, if you have very restricted privacy settings for your story, they still might not be able to see it even after being unblocked. You may need to review and potentially adjust those settings so that they can have access to your Snap Story again.
Generally, you won't get a direct notification from Snapchat when someone takes a screenshot of your story. But there are no foolproof ways to tell for sure. Some people might mention it to you if they choose to, but that's rare.
No, they can't. When you block a user, Snapchat ensures that they are cut off from seeing your stories. This is part of the privacy features of the app. By blocking, you are essentially saying that you don't want that person to have any form of access to your Snapchat content, and that includes your snap stories which are often a way of sharing your daily moments or thoughts with your friends or followers on the app.
One way is to directly ask him and tell him why you think he'd enjoy it. For example, mention that it shows something related to his interests or hobbies.
To see who viewed your Snapchat story, just open the app after posting the story. Usually, Snapchat will display a list of people who have viewed it. But keep in mind that not everyone's view might be shown immediately.