How do i add confirm password field to signup in universal login?
When you use the classic universal login experience you can fully customize the user interface. In general and by default a customized login page will use Lock and with Lock although you can perform some customizations you’re constrained to what Lock allows to configure and to my knowledge Lock does not support a password confirmation field at this time.
However, you can also implement the user interface with Auth0.js library which will not impose any constraints on the user interface you can implement so technically you can meet that requirement by customizing the login page with that library (see information about the two approaches at Centralized Universal Login vs. Embedded Login).