Custom title for Magnific Popup

As per documentation titleSrc:{} should be inside image:{} and you can use item.el.parents() instead of item.el.parent().

Corrected Code

$('.container').magnificPopup({
    delegate: 'article figure a',
    type: 'image',
    gallery:{enabled:true},
    image: {
        titleSrc: function(item) {
        return item.el.parents('article').find('h2').html() + item.el.parents('article').find('figcaption').html();
        }
    }
});