I mean the cube’s rotation relative to world space – if the player causes the cube actor to rotate, then the cube actor has a rotation relative to world space. It may be simplest to use “Unrotate Vector” to transform the “Impact Normal” vector into world space, then do the dot product with constant values corresponding to the x (1, 0, 0), y (0, 1, 0), and z (0, 0, 1) axes. See the attached
partial example. In the example, the node labeled “X” will be +1 if the face that was hit is in the direction of the cube’s local positive X axis, -1 if it is in the direction of the negative X axis, or 0 if it is in the direction of either the Y or Z axis. The node labeled “Y” will be +1 if +Y, -1 if -Y, or 0 if X or Z, and the node labeled “Z” will be +1 if +Z, -1 if -Z, or 0 if X or Y. Note that the above values may be slightly off due to floating point math, so you would want to check to see if it is “close enough” to 1, or -1, or 0, rather than exactly equal. There is a BP node that will do this called “Nearly Equal.”
If you are going to try to do anything in a 3D game, it will help you a lot to learn some vector math (in fact, I’d say you won’t get far at all and won’t have any fun if you don’t have at least a rudimentary understanding of how vectors work and what the dot product and cross product do). The Khan Academy has some lectures on vectors that seemed quite good.
Hope that helps.