To access the hand tracking data directly from the Unreal blueprint simply use the GetLatestFrame API to access the current hand tracking frame. This is accessible via the LeapComponent that you can see here:
To get at a finger transform from the skeletal mesh, either attach a scene component to the given socket on the skeletal mesh and use its transform as shown below:
or use the GetSocketTransform API on the skeletal mesh as shown here:
To find out more, see our Unreal Documentation here.