Magento 2 : Get the parent product id list page

<?php
    $productId = $block->stripTags($_product->getId(), null, true); // assign child product id
    $objectManager = \Magento\Framework\App\ObjectManager::getInstance();
    $product = $objectManager->create('Magento\ConfigurableProduct\Model\ResourceModel\Product\Type\Configurable')->getParentIdsByChild($productId);
       if(isset($product[0])){
           // here you will get parent product id  
           echo $product[0];
       }
?>

If you want to use this code at block file in Magento 2, then use below code snippet.

protected $_productTypeConfigurable;

public function __construct(
		\Magento\Catalog\Block\Product\Context $context, 
		\Magento\ConfigurableProduct\Model\ResourceModel\Product\Type\Configurable $catalogProductTypeConfigurable,
		array $data = []
	) {
		$this->_productTypeConfigurable = $catalogProductTypeConfigurable;
		parent::__construct($context, $data);
	}
public function getProductData($id){  // pass child product id in this function
		$parentByChild = $this->_productTypeConfigurable->getParentIdsByChild($id);
		if(isset($parentByChild[0])){
			$parent_id = $parentByChild[0]; //here you will get parent product id
		}
		return $parent_id;     
	}