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Try bellow code

<?php

namespace Mainf\Stickers\Block;

class Discount 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 _prepareLayout()
    {
        return parent::_prepareLayout();
    }

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

    public function getCurrentProduct()
    {       
        return $this->_registry->registry('current_product');
    }   

}
?>

Display current product data in your template (custom.phtml) file

if ($currentProduct = $block->getCurrentProduct()) {
    echo $currentProduct->getName() . '<br />';
    echo $currentProduct->getSku() . '<br />';
    echo $currentProduct->getId() . '<br />';       
}