How to Create a Conditional Format where the choice in one column makes a second column required

Here’s the scenario:

In Sharepoint 2013 (on-prem) I have a custom list.  The list has a Yes/No column called Ineligible.  What we want to do is make Qual__Ineligible a required field (user has to choose one of the available values) if the Ineligible column is YES.  If the Ineligible column is NO, then the Qual_Ineligible should be blank (if they aren’t ineligible, then we don’t need to know what qualification makes them ineligible.

I know how to do it in InfoPath forms, can I just modify the custom list in InfoPath?

I don’t know how to do it with jQuery or spservices, but would like to learn.  if someone can point me to the appropriate resources/information, I’d appreciate it.