Currently the tradeable status of rewards in Trainer Challenge are based on the tradeable status of the theme deck's contents used to unlock the reward.
The contents of a deck acquired via Trainer Tokens are non-tradeable, therefore the booster pack reward for completing 12 Trainer Challenge matches with the deck is also non-tradeable. Conversely, the contents of a deck acquired via Gems* or code redemption are tradeable, so the booster pack reward for completing 12 Trainer Challenge matches with the deck is also tradeable.
*Note: As of Oct. 30, 2018, the Pokémon TCG Online will begin phasing out the ability to purchase Event Tickets and Gems. For more information please see, "Event Ticket and Gem purchases ending."
Can’t find what you’re looking for? Click here to submit a service request form.