(1) sitting where there is the least motion - For example, in the centre of the backseat
(2) a semi-reclined position with the head braced is best
(3) focus on things straight ahead outside the car, i.e., avoid reading and avoid looking at passing by things
(4) avoid the following before or during travel - dairy products, salty and fatty foods, large meals
(5) wristbands and magnets may be helpful, but there is little information on their efficacy
It may be a fungal infection. Your doctor can send nail clippings for fungal culture in order to make a proper diagnosis.
If ankle clonus persists beyond 3 months of age, it may be a sign of neurodevelopmental disorder.