you have to go under the car for that, it is near the fish plate that holds the TC nuts, very hard to get, none of the japanese cars have engine number stamped anywhere on chasis plate or sticker(I maybe wrong but never seen any in vitz, fielder, axio) only the type is mentioned e.g 1SZ-FE, 2SZ-FE etc
The engine number comes with the auction sheet documents and customs GD and ETO uses the data from it to post the number in Excise record. Nothing special, just forget it and use the car