1) Yes the displacement occurs when you are moving in a train. Displacement is defined as the direct length between two points is called displacement. For example, if you are travelling from place A to place B then, The total direct length of your path from the start point A to B becomes displacement. The complete length of the path you traveled between the two A and B points is called distance.
2) When we travel in a circular motion and end back in the same place can be called motion. This is because you travel in the circular path and end at the same point only the displacement will be zero but the path you traveled will be considered as motion.