Luckily Jakub its not that complex. In the side view simply extend the lower control arm line in the plane of the wheel center. At the top of the strut draw a line normal to the strut center line axis in the side view to intersect the lower control arm line. The intersec is the longitudial view...
I am a bit thrown back by your post. The coordinate system taken in any problem should not alter the outcome of the problem. This piont is simply a randon piont of referance. I am not sure if in this debate they are comparing the assumption that the CG does not move in one ref and traking the CG...