Answered Ajax call to pull in resource or chunk?

Put what you want in the chunk. Then have a resource with the no template and only the chunk tags. You can even customize this more by passing data in the AJAX call and using a snippet instead of a chunk to get the data from the POST and load the appropriate chunk along with the data where it's needed. The AJAX call will return the processed chunk.

I'm working on something very similar, an application form that will pop up as an overlay when a button next to an item in a row of similar items is clicked. It fetches the form from a chunk in a form.html resource, with certain information already set in hidden fields. The form submission button is another AJAX trigger that submits the form to a formit.html resource, where the usual FormIt processing is done, and FormIt's output, either errors and the form again, or a thank-you success message, is returned to the same popup overlay on the same page.

https://rtfm.modx.com/revolution/2.x/case-studies-and-tutorials/loading-pages-in-the-front-end-via-ajax-and-jquery-tabs