It is possible to check who is the Original Trainer of a Pokémon in the Stats interface (as shown to the right).
This stat has no use in Battle, Breeding or evolving, but is needed to gain the trust of some specific Pokémon and use their secondary effect (i.e. The Lake Trio will only enchant the Ruby if the player is the Original Trainer).
How to change the Original Trainer?
It is not possible to change the Original Trainer of a Pokémon in Survival-mode. Once caught, the OT will stay the same forever.
This stat can only be modified by the use of a Pokémon Editor wand.