Can a "Response Required Email" step in a workflow be sent to a variable user?

John, an email user task cannot have a dynamic recipient at this time.

I would encourage you to use the form user task. The form can be very simple and only require a single response, but in my experience (which is vast) is a much better way to go for several reasons:

1 - You can get more than a single predefined response
2 - You can have the recipient be dynamic
3 - They can get push notifications in the Task Center App

I could go on, but in my experience everyone thinks they want the email user task until they've used it once. The user will get an email on their phone, click the button and it will launch Domo in the browser. They won't be logged in, so they'll have to go through the authentication flow, then their response is recorded and they can close the browser. Furthermore, if this is something with any frequency, they're having to go back through a crowded inbox to find the things that are waiting for them.

Task Center, both in the mobile app and Domo web app, provides a much more comprehensive and user friendly experience. If you need help with it, let me know.

Now, if you are hell bent using the email user task, there is some creativity that can accomplish it. You can dynamically add a user to a group, send the task to that group, and then after they complete it remove the user from the group. It can get messy and you could potentially have race conditions where multiple people are in the group, but it's a creative approach I saw someone use (before they realize the Form User Task just works better) that I figured might be worth mentioning.