You can often help a carsick dog by positioning the dog to see out the front of the vehicle in the direction of movement. This allows the eyes to help orient the confusing sensations from the ears. It also often helps to open one or more windows about three inches, to help equalize the air pressure.
Stress contributes to carsickness, and a dog who has lost a previous home via a car ride may be stressed by riding in your car at first. The same happens with dogs who have only been driven to the veterinarian's office for treatment, and never to places they enjoyed going.
The solution is very simple. If the dog has been sick in a car then estimate how long it was in the car before it was sick, say 20 minutes? Find a park about 5-10 minutes from home, preferably one just around the corner, even one within walking distance that the dog has been to before.... but this time drive there. Ideally have someone else in the car too to help keep him distracted. Keep him happy all the way to the park. When at the park do all the enjoyable things that the dog loves, fetch the ball, chase the Frisbee, frolic with dad, etc. The stay at the park doesn't need to be that long.... just as enjoyable as possible. Then drive the dog home soothing him all the way again and when home make just as much fuss of the dog as you did at the park. Finish the session with his meal or a treat if time and conditions permit.