<a href="#" data-quantity="1" data-product_id="103" data-product_sku="" class="cart-btn button product_type_simple add_to_cart_button ajax_add_to_cart"></a>
<input type="text" class="num-items" value="2">
jQuery('.inline-block').on('change', 'input.num-items', function(){
var test = $('a[data-quantity]').trigger('click');
console.log(test);
});