Q1: If I have 2 or fewer cards in my deck, does this Digimon’s When Digivolving effect activate?
Yes, it activates. In such cases, trash as many cards from your deck as is possible. Then, if you have a Tamer, this Digimon gets +3000 DP for the turn.
Q2: When using this card's When Digivolving effect to return cards from my trash to the bottom of my deck, is my opponent allowed to check what cards I am returning to my deck?
Yes. Cards in your trash are considered public information, so please let your opponent confirm which cards you're returning to your deck before you do so.
Q3: Can I use this card's When Digivolving effect to return 3 non-Digi-Egg cards to the bottom of my deck but choose to not give this Digimon +2000 DP?
No, you can't.
Lv.5 AeroVeedramon Zero P-047 P Ultimate | Vaccine | Holy Dragon [When Digivolving] Trash the top 3 cards of your deck. Then, if you have a Tamer in play, this Digimon gets +3000 DP for the turn. --- Inherited: [When Attacking] You may place 3 non-Digi-Egg cards from your trash at the bottom of your deck in any order to have this Digimon get +2000 DP for the turn.
Lv.5 AeroVeedramon Zero P-047 P Ultimate | Vaccine | Holy Dragon [When Digivolving] Trash the top 3 cards of your deck. Then, if you have a Tamer, this Digimon gets +3000 DP for the turn. --- Inherited: [When Attacking] By returning 3 non Digi-Egg cards from your trash to the bottom of your deck in any order, this Digimon gets +2000 DP for the turn.
Lv.5 エアロブイドラモン ゼロ P-047 P 完全体 | ワクチン種 | 聖竜型 【進化時】自分のデッキの上から3枚破棄する。その後、自分のテイマーがいるとき、このターンの間、このデジモンのDPを+3000する。 --- Inherited: 【アタック時】自分のトラッシュから、デジタマカード以外のカード3枚を、好きな順番でデッキの下に戻すことで、このターンの間、このデジモンのDPを+2000する。