2. How do someone veto a transaction which made by attacker where we can verify who's the owner or attacker without compromise owner privacy?
Bitcoin protocol have
neither veto system or way to verify who create the transaction.
As long as a tx isn’t confirmed, you have full control over it. You can cancel a tx (not cancel actually) in Electrum wallet if the tx isn’t yet confirmed. You can send the same input of your tx to another address by creating a tx with higher fee. But all that's possible till the tx pending (no confirmation).
Take note it's only possible if the transaction has RBF flag and your wallet have feature to "cancel" unconfirmed RBF transaction. Additionally, you need to notice that you made unwanted transaction before it's confirmed. It could be less than 10 minutes when mempool is near empty (less than 1MB) or you pay very high fees.