Передаем title в форму

gistfile1.txt

в чанке формы пишем
<div class="form-group">
    <input type="text" name="product" value="[[!+fi.product]]" class="form-control" readonly="readonly">
</div>

JS вешаем на кнопку
{ignore}
<script>
	$(document).ready(function() { 
		$('a.theme-btn.btn-style-five').on('click', function(){ 
			$('input[name="product"]').val($(this).data('title'));
		} );
	});
</script>
{/ignore}

Сама кнопка
<a data-fancybox data-src="#quick_order" href="javascript:;" data-title="{$_modx->resource.pagetitle}" class="theme-btn btn-style-five">Заказать</a>

Передать заголовок
var textContent = $('button').data('title');
$('h2.a-popup__title').text(textContent);

======================================================================================
вариант 2

<div class="col-md-6 pprev">
    <div class="pfon" style="background-image:url('{$serviceImg}')"></div>
    <div class="category-service-item-text plink row">
            <a href="{$uri}" class="ptitle2 pagetitle-services">{$pagetitle}</a>
            <a class="ptitle2 pmore_link" href="{$uri}">Читать дальше</a>
            {if $price}
                <div class="ptitle">Цена: {$price} руб.</div>
            {/if}
            <div class="zapis-services-btn" data-toggle="modal" data-target="#zapisservices">Купить</div>
    </div>
</div>

<script>
	$('.zapis-services-btn').on('click', function () {
		var parent = $(this).parent();
		var taga = $(parent).find('.pagetitle-services');
		$('#zapis-services-services').val($(taga).html());
		$('#zapis-services-url').val("[[!++site_url]]" + $(taga).attr('href'));
		$('#zapis-services-title').attr('href', $(taga).attr('href'));
		$('#zapis-services-title').html($(taga).html());
	});
</script>

в чанке ajaxform пишем
<a href="[[*uri]]" id="zapis-services-title" class="form_href-services">[[*longtitle:is=``:then=`[[*pagetitle]]`:else=`[[*longtitle]]`]]</a>

<div class="field-6">
	<input id="zapis-services-services" name="zapis-services-services" type="hidden" value="[[*longtitle:is=``:then=`[[*pagetitle]]`:else=`[[*longtitle]]`]]">
	<input id="zapis-services-url" name="zapis-services-url" type="hidden" value="[[!++site_url]][[*uri]]">
</div>