Where and how is the Porsche published ride height specification measured?

 

Dock,
The front ride height is measured from the bottom of the tension tie strut's attachment to the frame. There is a bolt head there. You measure from the bolt head surface to ground level.
The rear ride height is measure in a similar manner except it is from the milled surface of the bore hole in the rear suspension side sub-frame member.
It is each on the lift, much more difficlt on the ground.