How Does One Achieve Above Character GUI?

How would you create a gui above a players head?

Billboard GUIs are the way to go!

I use Billboard GUIs whenever I make nametags, and I really like them. If you're new to them, they may be a bit confusing. They're basically GUIs in the air. The issue a lot of people face is whenever the Billboards automatically resize, which holds a rather easy solution that I'll let you find yourself ;)

You could also a part welded to the head, and add a SurfaceGui, which makes a GUI on the part.

The previous answer is most likely the best solution for your needs. However, I see no harm in putting out an alternative solution, using the WorldToScreenPoint/WorldToViewportPoint functions of Camera.
These allow you to take any 3D point in the world and calculate its 2D position on screen. This allows for more control, if for example you want custom scaling logic or if you simply don't want to create a part to adorn it to.
Again, you will probably have better luck with BillboardGuis, but I might as well put this alternative out there.