Rulings
Q1: I have this Digimon and 1 purple Digimon in play. My opponent's Digimon attacks, and its When Attacking effect deletes my purple Digimon. Can this Digimon now block the attack?
No, it can't. If your purple Digimon was deleted by a When Attacking effect, then this Digimon won't have Blocker when reaction timing arrives, and won't be able to activate Blocker to block the attack.
Data Sources
EN
Official English Card Listworld.digimoncard.com
Lv.4 Gatomon P-031 P Champion | Vaccine | Holy Beast [Opponent's Turn] While you have a purple Digimon in play, this Digimon gains <Blocker>. (When an opponent's Digimon attacks, you may suspend this Digimon to force the opponent to attack it instead.)[On Play] If you have 3 or fewer security cards, trigger <Recovery +1 (Deck)>. (Place the top card of your deck on top of your security stack.)
A
Official English (Asia) Card Listen.digimoncard.com
Lv.4 Gatomon P-031 P Champion | Vaccine | Holy Beast [Opponent's Turn] While you have a purple Digimon in play, this Digimon gains <Blocker>. (When an opponent's Digimon attacks, you may suspend this Digimon to force the opponent to attack it instead.)[On Play] If you have 3 or fewer security cards, trigger <Recovery +1 (Deck)>. (Place the top card of your deck on top of your security stack.)
W
DCG Wikidigimoncardgame.fandom.com
Lv.4 Gatomon P-031 P
Champion | Vaccine | Holy Beast
[Opponent's Turn] While you have a {{Colour|purple}} Digimon in play, this Digimon gains <Blocker>.
[On Play] If you have 3 or fewer security cards, <Recovery +1 (Deck)>.JP
Official Japanese Card Listdigimoncard.com
Lv.4 テイルモン P-031 P 成熟期 | ワクチン種 | 聖獣型 【相手のターン】紫の自分のデジモンがいる間、このデジモンは≪ブロッカー≫（相手のデジモンがアタックしたとき、このデジモンがアクティブ状態ならレストさせることでアタックの対象をこのデジモンにする）を得る。【登場時】自分のセキュリティが3枚以下のとき、≪リカバリー+1《デッキ》≫（自分のデッキの上からカードを1枚セキュリティの上に置く）。