Discarding after picking up discard pile in Canasta
There is no rule specifying what type of cards you discard so it is up to the player to decide if they want to discard a dead card or a wild card.

Canasta Rules


  When a player has melded his cards, he ends his turn by discarding a card. At that point, his melded cards are checked to see if they conform to the canasta rules. Discarding a card is not necessary if the player can go out by melding all of his cards.