In official games, discards are shown in the middle of the screen in chorological order.
When using the Practice mode, you’ll need to choose between viewing the hand suggestions or the discards - since there isn’t enough space on the screen to show both at the same time. When viewing the hand suggestions, click the "Show Discards" button (towards the bottom left of the screen) to see the discards.
Note that in practice mode, discards are grouped and counted. You’ll be able to easily click back and forth between viewing the discards and viewing the hand suggestions.