If a car is travelling 200mph on top of a train also travelling at 200mph....?

How fast are you travelling?

yes but no work is done by the car the kinetic energy is spend is minimal then only force on the car is friction from the air

If the direction is the same, the car is travelling at 200mph relative to the train, 400mph relative to the ground, the person in the car is stationary relative to the car. Its all relative.

400 mph until you reach the front of the train, or 0 mph if your going from front to back

well it depends on which direction the car is going...
if it is going the same way as the train the wind will blow it back - innit

congratulations, you have discovered relativity

it was this sort of thought experiment which led to Einstein's theory of relativity.

and it all depends on relative directions and relative points of reference

the earth is spinning at 1041 mph at the equator
it is orbiting the sun at 69,360 mph
the entire solar system is moving at 43,200 mph relative to Lambda Herculis
The Solar system is also orbiting around the Galaxy at an estimated 446,400 MPH.

depends on where u r. if ur not in the car or the train then you can be traveling at anyspeed. if ur in the train ur traveling at 200mph. if ur in the car a few things would effect ur speed.
1) if the car and train are traveling in opposite directions then u r technicly standing still because the speeds of the train and car negate each other. but if u wanted to get urself to travel at 200mph then ud have to accelerate the cart to 400mph to negate and reverse the speed of the trains effect on you.
2) if the train and the car are traveling in the same direction then two things can happen. if the car is off or the engine isnt going you are traveling at 200mph. BUT if the cars engine is running and the speedometer reads 200mph then u have to take the combined total of the train and the car speed to get ur speed. which would be 400mph

Where am I?

At the moment there is a passenger in a plane travelling at 500mph walking along the aisle at 2mph. But I am sat at my computer and feel like I am not travelling at all.

I think you need to tell all us poor souls what the situation is.Is the car travelling at 200 mph relative to the train? and if so is in same direction or opposite direction to this super train?

200 mph as nether train or car are faster than 200 mph.