Hey there im not quite sure if i get you right but could it be that you are looking for Get Actor Location, which gets you the LocationVector of your desired object?
If you mean with relative Position between Character and cube the vector between them you could substract bot actor location and its returning the vector. F.e. From Cube(Point A) to Character(Point B) you could substract B-A and you get the direction vector (DirV). The relative positionnow would be: PointA + DirV = PointB
Was that you intention?
kind regards