<select id="parent-{{product.id}}"><option>124</option></select>

jquery("#parent-{{product.id}}").hide();
   jquery("#parent-{{product.id}}").show();

id= parent-{{product.id}}

<div class="select">
<select id="product-select-{{ product.id }}{{ product-form }}{{ section.id }}{{ block.id }}" name="id" class="multi_select">
  {% for v in product.variants %}
      <option {% if v == variant %} selected="selected" {% endif %} data-sku="{{ v.sku }}" value="{{ v.id }}">{{ variant.title }} - {{ v.price | money_with_currency }}</option>
  {% endfor %}
</select>