Hi Kenzo,
To add a button, you have to edit the view product / show_default.php, or show_reversed.php, or show_tabular.php depending on which one your are using.
To edit this view, go in HikaShop > Display Views.
Then you can add something like:
<span id="hikashop_product_contact_us" class="hikashop_product_contact_us">
<input type="button" onclick="location.href( 'your contact page');" />
</span>
Just after the code:
<span id="hikashop_product_price_main" class="hikashop_product_price_main">
<?php
if ($this->params->get('show_price')) {
$this->row = & $this->element;
$this->setLayout('listing_price');
echo $this->loadTemplate();
}
?>
</span>
To place it next to the 'add to cart' button.