What syntax do I use to add a form element in an email message?

Summary:

We want to display (in an email message) the date selected in a form using the date picker field type.

Content (please ensure you mask any confidential information):

We have a form that is submitted as part of an activity. The form has a 'Date and Time' form element so the user can pick the date from the calendar (date picker). The default field name is "form_element#1". What syntax should I use if I want to display the selected date value in an email message? I tried a few variations but they are not working.

Version (include the version you are using, if applicable):