Looks like you're using a custom CB template and you've replaced the PHP files and it's out of date. It doesn't have the data attributes. Switch back to default template and it should work fine. Your alternative is to just add the data attribute yourself to your fields HTML and grab it in your JS. For example if you directly added it to the cbEmailUserSubmit as follows.


Then the below jQuery can just grab it from there.

I will check that but can I use overrides to the original template without creating a custom one? If yes, where do I find the overrides?

Depends on what you're trying to override. If you just want to override the CSS then you can use the Template Builder built into CB Template Changer to generate custom templates. This avoids touching the PHP and only overrides whatever CSS you want.

CB > Plugin Management > CB Template Changer > Templates is where you can manage custom templates. Those generated there are CSS only custom templates and they do not override the PHP or HTML of the core template. Once created you can assign as the default profile template from there or within CB > Configuration > User Profile.