Showing syntax error

You can make it into a shortcode:

add_shortcode( 'schema_data', function () {
    ob_start();
    ?>

<div itemscope itemtype="http://schema.org/Review">
<div itemprop="itemReviewed" itemscope itemtype="http://schema.org/LocalBusiness">
<span itemprop="name">Quest Realty</span>
</div>
<div itemprop="name">Quest-Real Estate Listings, Home for sale, Housing Data</div>
<div itemprop="description">Your destination for all real estate listings and rental properties. Quest-amwaj.com provides comprehensive school and neighborhood information on houses/flats/apartments/commercial areas for rent/sale.</div>
<div itemprop="reviewbody"> Quest realty is a reliable real estate agency for renting as well as buying properties.</div>
<div itemprop="author" itemscope itemtype="http://schema.org/Person">Written by: <span itemprop="name">CArrie Hill</span></div>
<div itemprop="author" itemscope itemtype="http://schema.org/Thing">
<span itemprop="name">Properties in Bahrain</span></div>
<div><meta itemprop="datePublished" content="2015-05-15">Date Published: 15/05/2015</div>
<div itemprop="reviewRating" itemscope itemtype="http://schema.org/Rating">
<meta itemprop="worstRating" content="0"><span itemprop="ratingValue">4.5</span> / <span itemprop="bestRating">5</span> stars</div>
</div>

    <?php
    return ob_get_clean();
} );

Then you can use the [schema_data] shortcode in your posts and pages.

If you’re interested in finding out how this PHP code works, I recommend you read about output buffering and shortcodes.

What version of PHP are you using?

Are you sure that this is all of the code that you’re using, and that the error isn’t coming from elsewhere? I have tried running this code multiple times, and I don’t know you could be getting that error from ob_start()