On the registration page, open the server behaviors panel and double click the Server Validation server behavior.
select the Required validation type. Click the lightning bolt next to Server Variable and select the aditional field that should be required, then click the plus button to add it to the list of validations.
repeat this for each additional form element that should be required.
you will then need to create the validation error massages, type the error test next to the form element, highlight the error text then go to WebAssist -> Forms -> Validation -> Validation Show If.
Select the validation to trigger the error message, then click the plus button and click ok.
Use the same steps to create the validation error messages for the other elements.