Number of sold items as product attribute

Q: Is it possible to show a number of already sold items in product description and it should increase automatically after each transaction?

A: There's a meta that tracks total sales on a product: total_sales. Use something like this to echo the total sales:
echo get_post_meta(PRODUCT_ID_HERE, '_js_total_sales', true).

You have to put it inside the PHP files or use this plugin to allow PHP in your posts.