Thievery
Damage = [Number of successful Steals * Zidanes Speed] / 2

With 50 Speed Zidane will need 400 successful steals to make Thievery deal 9,999. If his Speed is lower, you'll need more steals.

Dragon Crest
Damage = No. of dragons killed by the party * No. of dragons killed by the party

100 dragons will make Dragon Crest deal 9,999 damage

Frog Drop
Damage = No. of frogs caught * Quina's level

At Lv99 you'll need 101 frogs to deal 9,999 damage.