What is the preferred clock, does choice of clock define the laws of physics?
How do you pick a preferred clock here?
You get another clock. This is essentially the reason that Hafele–Keating used an ensemble of four clocks in their famous experiment. The average of four clocks is more accurate than a single clock and if one clock has a malfunction then it will be apparent which clock is problematic. Preferred clocks are ones that consistently agree with each other the best.
To begin with, we must eliminate the possibility that one of the two clocks is broken. Once we are sure that is not the case, the laws of physics indeed depend on our choice of clock. It happens to be that in the case of our universe, we have principles that say that the laws of physics are the independent of the choice of reference frame. However, remember that we had to establish first that the speed of light was the same in all inertial frames, before we could postulate that there was no preferred inertial frame. This is certainly not an axiom we can just start with.