This addon will simply add the target of your target to the default game tooltip.
The target will update if their target changes, so you do not have to move your cursor on and off the target to get updates regarding their target.
If their target is you, it will display "<YOU>" instead of your characters name.
I was using one of the larger tooltip mods that let you add tons of stuff to your tooltip, but I found that all I really cared about was the target of my target and the location of the tooltip, the rest of the addon was just bloat. So for the latter I found ToolTipOnMouse, and for the former I decided to write my own, simple and to the point.