In this post I am going to explain how to get current customer group id in PrestaShop 1.7.

1) Inside module or controller file (php)

if ($this->context->customer->isLogged()) {
	$customerGroupId = $this->context->customer->id_default_group;
	echo $customerGroupId . "<br>";
	// Do something here
} else {
	// Do something here
}

2) Inside template file (tpl)

{if $customer.is_logged}
    {$customer.id_default_group}
{/if}