JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.4.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/magnific-popup.js/1.1.0/jquery.magnific-popup.min.js"></script>
<a href="/form/" class="popup-form" data-v="Значение дата">Заказать звонок</a>

JavaScript

$('.popup-form').magnificPopup({
  type: 'ajax',
  tClose: 'Закрыть',
  tLoading: 'Загрузка',
  callbacks: {
    open : function(){
      var mp = $.magnificPopup.instance,
          t = $(mp.currItem.el[0]);

      console.log( t.data('v') )
    },
    close: function() {
    }

  }
});