Rulings
Q1: Can this card's On Play effect place cards in this Digimon's digivolution cards if I don’t have both a SkullKnightmon and DeadlyAxemon in either my hand or trash?
Yes. You don't have to place both a SkullKnightmon and a DeadlyAxemon. You can also place either of them on their own from either your hand or trash in this Digimon's digivolution cards.
Q2: Can this card's On Play effect place a SkullKnightmon in my hand and a DeadlyAxemon in my trash in this Digimon’s digivolution cards?
Yes. You can mix and match SkullKnightmon and DeadlyAxemon from both your hand and trash to place in this Digimon’s digivolution cards.
Q3: If I have both SkullKnightmon and DeadlyAxemon in this Digimon’s digivolution cards, does this card’s All Turns effect require me to play both?
No. The effect reads, “you may,” so you can choose whether to play them. However, if both SkullKnightmon and DeadlyAxemon are in digivolution cards, you must choose to either play both of them or play none of them.
Q4: When does the All Turns effect of the Digimon trigger?
The All Turns effect triggers and activates immediately prior to the Digimon being deleted. In this way, the All Turns effect has the same timing as effects that say, “when this Digimon would be deleted”.
Q5: Can this card's On Play effect be placed in the digivolving card unless I have both "Skull Knightmon" and "Deadly Axmon" in my hand or trash?
No. Even if you only had either "Skull Knightmon" or "Deadly Axmon", you can still place them on the digivolution card.
Q6: Can this card's On Play effect put "Skull Knightmon" from my hand and "Deadly Axmon" from my trash to digivolving card respectively?
Yes, you can put "Skull Knightmon" and "Deadly Axmon" from both hand and trash to digivolution card.
Q7: For this card's All Turns effect, if there are both "Skull Knightmon" and "Deadly Axmon" as digivolves, do I always have to play both?
No, it is "can appear" and you can choose whether or not to have it play. However, if you have both "Skull Knightmon" and "Deadly Axmon" as digivolution cards, you can either play both of them or none of them.
Data Sources
Lv.5 DarkKnightmon BT7-063 SR Ultimate | Virus | Dark Knight [On Play] You may place 1 [SkullKnightmon] and/or 1 [DeadlyAxemon] from your hand and/or trash in this Digimon's digivolution cards in any order. [All Turns] When this Digimon is deleted, you may play 1 [SkullKnightmon] and/or 1 [DeadlyAxemon] from this Digimon's digivolution cards suspended without paying their memory costs.
Lv.5 DarkKnightmon BT7-063 SR Ultimate | Virus | Dark Knight [On Play] You may place 1 [SkullKnightmon] and/or 1 [DeadlyAxemon] from your hand and/or trash in this Digimon's digivolution cards in any order. [All Turns] When this Digimon is deleted, you may play 1 [SkullKnightmon] and/or 1 [DeadlyAxemon] from this Digimon's digivolution cards suspended without paying their memory costs.
Lv.5 DarkKnightmon BT7-063 SR ultimate | Virus | Dark Knight [On Play] You may place 1 [SkullKnightmon] and 1 [DeadlyAxemon] from your hand and/or trash in this Digimon's digivolution cards in any order. [All Turns] When this Digimon would be deleted, you may play 1 [SkullKnightmon] and 1 [DeadlyAxemon] from this Digimon's digivolution cards suspended without paying their memory costs.
Lv.5 ダークナイトモン BT7-063 SR 完全体 | ウィルス種 | 暗黒騎士型 【登場時】自分の手札かトラッシュから、「スカルナイトモン」と「デッドリーアックスモン」1枚ずつを好きな順番でこのデジモンの進化元に置ける。 【お互いのターン】このデジモンが消滅するとき、このデジモンの進化元から、「スカルナイトモン」と「デッドリーアックスモン」1枚ずつをコストを支払わずにレスト状態で登場できる。