I haven’t been doing UXP for a while so I forget what’s in the transform object, but I believe the skew info is in the smartObjectMore.nonAffineTransform section. I think it’s like rotation though in that you have to manually compare the affine transforms points compared to the default dimensions to calculate what kind of skew is going on.
The vertex coordinates in transform and nonAffineTransform are exactly the same. Scale, skew and rotation have been applied to the object. I did not find how to separate and extract this data, although it is visible in the info panel when pressing ctrl + t