The ToroCraft’s Damage Indicator mod will allow you to see the amount of health of any mob that you see in front of you. This way you can understand how much health any mob has left.
Mod ToroCraft’s Damage Indicators for Minecraft 1.14.4/1.12.2
The indicator is located in the upper left corner, it looks pretty nice and informative. Dealing damage to a mob, you can see the amount of damage that you caused, it is really incredibly convenient and cool.