How can I draw hand skeletons?

You can take a look at how it can be done in Detecting Hand Poses with Vision sample code.
The CameraView class has an overlayLayer property that displays points detected by VNDetectHumanHandPoseRequest and converted to UIKit coordinates.
In the sample we only display two points corresponding to the thumb and index finger tips.
However, VNRecognizedPointsObservation provides points for all supported joints.
In your code you can use these points to build UIBezierPath that consists of circles and line segments representing a "hand skeleton".