Q1: When my opponent has 2 Digimon, can this card's On Play When Digivolving effect give both of of my opponent's 2 Digimon -3000 DP?
No, it can't. The effect only targets 1 of your opponent's Digimon.
Lv.5 Knightmon P-111 P Ultimate | Data | Warrior <Blocker> [On Play] [When Digivolving] 1 of your opponent's Digimon gets -3000 DP for the turn for each of your Digimon. --- Inherited: [All Turns] [Once Per Turn] When another Digimon attacks, you may play 1 yellow or black level 3 Digimon card from your hand without paying the cost.
Lv.5 Knightmon P-111 P Ultimate | Data | Warrior <Blocker> [On Play] [When Digivolving] 1 of your opponent's Digimon gets -3000 DP for the turn for each of your Digimon. --- Inherited: [All Turns] [Once Per Turn] When another Digimon attacks, you may play 1 yellow or black level 3 Digimon card from your hand without paying the cost.
Lv.5 Knightmon P-111 P Ultimate | Data | Warrior <Blocker> [On Play] [When Digivolving] 1 of your opponent's Digimon gets -3000 DP for the turn for each of your Digimon. --- Inherited: [All Turns] [Once Per Turn] When another Digimon attacks, you may play 1 {{Colour|black}} or {{Colour|yellow}} level 3 Digimon from your hand without paying the cost.
Lv.5 ナイトモン P-111 P 完全体 | データ種 | 戦士型 ≪ブロッカー≫ 【登場時】【進化時】ターン終了まで、相手のデジモン1体を自分のデジモン1体ごとにDP-3000。 --- Inherited: 【お互いのターン】[ターンに1回]他のデジモンがアタックしたとき、自分の手札から、黄/黒のLv.3のデジモンカード1枚をコストを支払わずに登場できる。