If all of the workflows are sending email to that email address you're looking for, you could narrow down your search by looking at the email server in the Workflow Administration Console, and seeing which workflows are using that email server.
https://www.laserfiche.com/support/webhelp/Laserfiche/10/en-US/administration/#../Subsystems/LFWorkflow/Content/Resources/Admin Console/E-mail Node.htm
If it's an internal email, and you're in charge of the email server, there might be a way to get the email server Workflow is using to automatically reject a connection if an attempt is made to send to that specific email address. Then you'd see all the relevant workflows throw errors.