How to get product category id on product detail page Magento 2

Please use below code :

<?php 
$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$product = $objectManager->get('Magento\Framework\Registry')->registry('current_product');
$categories = $product->getCategoryIds(); /*will return category ids array*/
foreach($categories as $category){
    $cat = $objectManager->create('Magento\Catalog\Model\Category')->load($category);
    echo $cat->getName();
    }

?>

Try this,

Create a custom module like below code.

create a module block file to get current category name.

<?php
namespace Namespace\Modulename\Block;
class Blockname extends \Magento\Framework\View\Element\Template
{
    protected $_registry;

    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        \Magento\Framework\Registry $registry,
        array $data = []
    )
    {
        $this->_registry = $registry;
        parent::__construct($context, $data);
    }


    public function getCurrentCategory()
    {
        return $this->_registry->registry('current_category');
    }

}
?>

create a phtml file with below code

<?php if ($currentCategory = $block->getCurrentCategory()): ?>
    <div class="detail-category-name">
        <?php echo $currentCategory->getName(); ?>
    </div>
<?php endif; ?>

call above phtml file via xml file.

<referenceContainer name="product.info.main">
            <block class="Namespace\Modulename\Block\Blockname" name="product.category.name" template="Magento_Catalog::product/view/yourfilename.phtml" >
            </block>
</referenceContainer>

And finally you can see category name just above product name on product detail page.