You don’t need to be a C++ wizard to do this.
Get the door’s right vector. If your door is orientated with the door knob pointing in the X axis, you can get the door’s right vector by doing: GetTransform().GetUnitAxis(EAxis::Y);
Then you dot product the ImpactNormal() and the right vector of the door in world space. This will tell you the angle between the ImpactNormal() and the door’s orientation. From that you can dynamically figure out which side of the door the ray hit.
I think you should do some research on dot and cross product. Most game programming involves in-depth math and trigonometry knowledge.