//Go to(windows style path) joomla root/components/com_k2/views/item/view.html.php  
// and comment line from 445 to 455
/*
$document->setMetaData('og:url', $uri->toString());
        $document->setMetaData('og:title', htmlspecialchars($document->getTitle(), ENT_QUOTES, 'UTF-8'));
        $document->setMetaData('og:type', 'Article');
        $facebookImage = 'image'.$params->get('facebookImage', 'Small');
        if ($item->$facebookImage && JFile::exists(JPATH_SITE.$item->$facebookImage))
        {
            $image = substr(JURI::root(), 0, -1).str_replace(JURI::root(true), '', $item->$facebookImage);
            $document->setMetaData('og:image', $image);
            $document->setMetaData('image', $image);
        }
        $document->setMetaData('og:description', htmlspecialchars(strip_tags($document->getDescription()), ENT_QUOTES, 'UTF-8'));
*/

For joomla root/components/com_k2/views/latest​/view.html.php

comment line from line 256 - 261
// Set Facebook meta data
/*
        $document = JFactory::getDocument();
        $uri = JURI::getInstance();
        $document->setMetaData('og:url', $uri->toString());
        $document->setMetaData('og:title', (K2_JVERSION == '15') ? htmlspecialchars($document->getTitle(), ENT_QUOTES, 'UTF-8') : $document->getTitle());
        $document->setMetaData('og:type', 'website');
        $document->setMetaData('og:description', strip_tags($document->getDescription()));
*/

For joomla root/components/com_k2/views/itemlist/view.html.php  line 690 to 701

// Set Facebook meta data
/*
		$document = JFactory::getDocument();
		$uri = JURI::getInstance();
		$document->setMetaData('og:url', $uri->toString());
		$document->setMetaData('og:title', (K2_JVERSION == '15') ? htmlspecialchars($document->getTitle(), ENT_QUOTES, 'UTF-8') : $document->getTitle());
		$document->setMetaData('og:type', 'website');
		if ($task == 'category' && $this->category->image && strpos($this->category->image, 'placeholder/category.png') === false)
		{
			$image = substr(JURI::root(), 0, -1).str_replace(JURI::root(true), '', $this->category->image);
			$document->setMetaData('og:image', $image);
			$document->setMetaData('image', $image);
		}
		$document->setMetaData('og:description', strip_tags($document->getDescription()));

*/