enter email address twice

I am not sure I understood your question correctly. Do you want to have another textbox where your user has to input the email address again and validate if both the email addresses are same? If yes, you can refer this guide to add email validation: https://www.jotform.com/help/147-Adding-an-Email-Confirmation-Field

If you are referring to something else, could you please explain more about your requirement so that we can assist you accordingly?

We will wait for your response.