Woocommerce – Print Product’s Custom Field In Email

the longsku is regular wordpress post meta, so you can simply call that with get_post_meta.

get_post_meta takes three arguments:

• post_id (which is already available in $_product)]
• meta key (‘longsku’ in your case)
• and a boolean to return a single string (true). if not set, it returns an array, but since the meta key is just a single value you can use true

this should do the trick for your longsku:

echo get_post_meta($_product->id,'longsku',true);