How can I make fields required based on user's answers?

Hi There,

i need the user to at least fill in one of the column as mandatory

- Email address OR contact number

how do i do that?

Thank you for contacting us.

We have a feature which exactly meet your requirement. This feature is enable/require condition logic where you can find more details at the following user guide. 

https://www.jotform.com/help/367-How-to-Make-a-Field-Required-Based-on-User-s-Answer

For your case, you need to set following conditions:

The above conditions work on the principle that if one of the fields are filled, the other field becomes not mandatory. However, please do not forget to make require both fields. Here is the demonstration of this feature:

If you have more questions, please do not hesitate to contact us. We would be pleased to assist you for any issue you may have.