Previously I have been able to position GoogleAds within the content on other websites by inserting the code in the correct place in the file single.php or page.php.
However the single.php file in Sparkling is very short and it is not possible to position an ad in the correct place.
If you want to display it in the post content then you can add it on line number 47 in the Sparkling child theme file /sparkling/template-parts/content-single.php before the following code.
<?php the_content(); ?>
If you want to display it in the page content then you can add it on line number 27 in the Sparkling child theme file /sparkling/template-parts/content-page.php before the following code.
The mistake I was making was to make the changes to a copy of content-single.php in the sparkling-child theme folder. After making the changes to a copy of content-single.php in the sub-folder wp-content/themes/sparkling-child/template-parts/, the issue was resolved.
The Adsense Ads are now positioned perfectly at the top of the post content but just below the title? i.e. At the top of the first paragraph.