Why isn’t comment validation working?

Add code in your theme function.php file

function comment_validation_init() {
if(is_single() && comments_open() ) { ?>

jQuery(document).ready(function($) {
$(‘#commentform’).validate({

rules: {
  author: {
    required: true,
    minlength: 2
  },

  email: {
    required: true,
    email: true
  },

  comment: {
    required: true,
    minlength: 20
  }

},

messages: {
  author: "Please fill the required field",
  email: "Please enter a valid email address.",
  comment: "Comments required minimum 20 characters."
},

errorElement: "div",
errorPlacement: function(error, element) {
  element.after(error);
}

});
});
</script>
<?php
}
}
add_action('wp_footer', 'comment_validation_init');