I have made various transactions with my wallet using bitcoind. If I lose my wallet (and private key) and somebody else somehow knows my private key and does some transactions, is it possible for me to somehow get a list of those new transactions?
If you have your wallet.dat in the Bitcoin core and someone else for some reason knows a private key that is associated with this wallet.dat, this person can spend the Bitcoins of that private key in basically, any other wallet, if this person does that, you will see this transaction in your Bitcoin core as the type "Sent to".
If you like to test it you can type
listunspent in your Bitcoin core, then you will see the addresses with an amount to be spendable, then you can copy any of these addresses and take the private key for that address using the command
dumpprivkey address, take this private key and import in any other wallet then send the Bitcoin to some other wallet.
If you have a list of old transaction IDs for transactions in which you received money, you can use those in one of the blockchain explorers to find the Bitcoin addresses of the transaction outputs. You can then see if those outputs have been subsequently spent. You will be able to see the transaction-IDs of the transactions that spend the outputs.