a person sitting in the compartment of a train moving with a uniform speed throws a ball in the upward direction.What path of the ball will appear to him?What to a person standing outside?

The person who is sitting inside the train, he/she will observe the vertical motion only because the object and the person both are moving with same velocity in horizontal direction.

For the person outside the rain path would be parabolic in nature.
Because person outside the train is still but the object have constant horizontal velocity and varying vertical velocity.