Q1: Can the When DigivolvingWhen Attacking effect of this card be chosen by either myself or opponent's Digimon?
Yes, you can choose either your own or opponent's Digimon.
Q2: Can this card in Breeding Area get the trait: "Three Musketeers" by Your Turn effect?
No, you cannot get the trait: "Three Musketeers". In Breeding Area, you cannot trigger/activate any effect other than the Breeding icon.
Lv.4 Deputymon EX7-010 R Champion | Vaccine | Mutant [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [When Digivolving] [When Attacking] [Once Per Turn] You may trash any 1 Option card from 1 Digimon's digivolution cards. [Your Turn] This Digimon gains the [Three Musketeers] trait. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.4 Deputymon EX7-010 R Champion | Vaccine | Mutant [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [When Digivolving] [When Attacking] [Once Per Turn] You may trash any 1 Option card from 1 Digimon's digivolution cards. [Your Turn] This Digimon gains the [Three Musketeers] trait. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.4 Deputymon EX7-010 R Champion | Vaccine | Mutant [Digivolve] Lv.3 w/[Three Musketeers] in text: Cost 2 [When Digivolving] [When Attacking] You may trash any 1 Option card from 1 Digimon's digivolution cards. [Your Turn] This Digimon gains the [Three Musketeers] trait. --- Inherited: [Your Turn] This Digimon gets +2000 DP.
Lv.4 リボルモン EX7-010 R 成熟期 | ワクチン種 | 突然変異型 「三銃士」の記述があるLv.3:コスト2 【進化時】【アタック時】[ターンに1回]デジモン1体の進化元から、オプションカード1枚を選んで破棄できる。 【自分のターン】このデジモンは特徴:「三銃士」を得る。 --- Inherited: 【自分のターン】このデジモンをDP+2000。