The best way is to actually make the function you need. It’ll work for any vector (2d or 3d).
You need to INPUT TWO DIRECTION VECTORS in WORLD SPACE.
First. Make a new function.
Make it have 2 inputs - VectorA and VectorB - and one output - a float.
Take the two vector values and normalize them.
Then take the two results and find the Dot product.
Then use the ACos Node to find the inverse Cos of the Dot product.
Voila.
