Countdown Enemy HP

I was wondering if it's possible to show the amount of HP the enemy has remaining when being hit instead of the damage we're doing. I remember this was a feature in the olden clients and I searched a bit around and thought this was maybe something easy to implement and tried it myself.
So far, no results.
I should say I have absolutely no experience or knowledge in coding whatsoever.

If anyone could guide me in the right direction, or show me how to implement this, I would be really thankful.
Thank you.

Any help anyone?