How do I prepopulate an email input if it doesn't contain a name attribute?

Normally, all regular text fields have a unique name and can be seen in the Chrom Devtools or Firebug.

It is possible that you are referring to a widget field. Are you referring to this form (https://www.jotform.us/form/71448612484157)?

I cloned this form and I can see that the "Player Email" field is a widget. Please follow the guide below in order to get the Unique Name of this widget field:

1. In the Form Builder, select the widget and then click the "Properties" button.

2. Go to "Advanced" tab and click the "Field Details" button.

3. Please copy the "Unique Name". You can use this for prepopulating the fields.

Here's the result:

 

Hope that helps. Thank you.