How can I block an I.P address that is sending spam to my jot form?

How can I block an I.P address or an email address that is sending spam to my jot form?

Unfortunately, there is not a way to block an IP address from submitting your form, you could only limit the submissions based on the number allowed from an IP address or based on a form question. 

Here're the guides that will help you with this: 

How-to-Set-Unique-Submissions-on-a-Form

How-to-set-Form-Limits-Based-on-a-Unique-Question

If you have embedded your form in a website then you could implement a custom script as  well to block the website when the IP address is used.