-snip-
Providing the transaction ID alone isn't that solid IMO, it's too easy "fake" the change address by using "coin control" or "pay to many" option/command.
I do not have anything left of Wallet A. I do have Wallet B in my possession.
So I do not know how to show the master public key without having anything left of wallet A. Anyway, I would need a pro to help me. I am really not experienced enough.
Hmm, like I said, it will be hard to prove that input1 and output2 (
change address) belongs to walletA just from that single transaction.
ChainAnalysis and other pro blockchain forensics will basically do a guesswork here unless you have used those addresses together in one transaction (
inputs).
Consider hiring another pro: Professional Data recovery; to be able to restore walletA from the drive where it was deleted;
if it's a hardware device, nevermind.