

Q1: Which effect activates first, a When Digivolving effect on an opponent's Digimon that digivolved, or this card's All Turns effect?
They trigger simultaneously, so the turn player activates their effect first.
Q2: When does this card's All Turns effect trigger, exactly?
It will trigger when a Digimon digivolves by an effect such as the effect on P-103 Offense Training. It won't trigger for effects that aren't digivolution effects, such as BT4-011 Agunimon's effect that treats a Tamer as a level 3 red Digimon or BT6-060 Deputymon's effect that allows digivolution requirements to be ignored.
Lv.6 Reapermon BT20-078 U Mega | Virus | Cyborg <Collision> <Blocker> [All Turns] [Once Per Turn] When effects digivolve your opponent's Digimon, <De-Digivolve 1> 1 of your opponent's Digimon. [On Deletion] Delete 1 of your opponent's play cost 4 or lower Digimon or Tamers. (Rule) Trait: Has [Ghost] Type. ---
Lv.6 Reapermon BT20-078 U Mega | Virus | Cyborg <Collision> <Blocker> [All Turns] [Once Per Turn] When effects digivolve your opponent's Digimon, <De-Digivolve 1> 1 of your opponent's Digimon. [On Deletion] Delete 1 of your opponent's play cost 4 or lower Digimon or Tamers. (Rule) Trait: Has [Ghost] Type. --- -
Lv.6 Reapermon BT20-078 U mega | Virus | Cyborg <Collision> (During this Digimon's attack, all of your opponent's Digimon gain <Blocker>, and the opponent blocks if able.) <Blocker> [All Turns] [Once Per Turn] When effects digivolve your opponent's Digimon, <De-Digivolve 1> 1 of your opponent's Digimon. [On Deletion] Delete 1 of your opponent's play cost 4 or lower Digimon or Tamers. (Rule) Trait: Has [Ghost] Type.
Lv.6 ゴクモン BT20-078 U 究極体 | ウィルス種 | サイボーグ型 ≪衝突≫≪ブロッカー≫ 【お互いのターン】[ターンに1回]相手のデジモンが効果で進化したとき、相手のデジモン1体を≪退化1≫。 【消滅時】登場コスト4以下の相手のデジモン/テイマー1体を消滅させる。 〈ルール〉特徴:タイプ「ゴースト型」を持つ。 ---