When I created the wallet I did not write the mnemonic words because I thought I can find it later via a command line, but then I could not find such a command.
Is there any way to get the mnemonic words again? or directly backup the full wallet to a disk file? like the BTC wallet.
I’d be very careful with a wallet you can’t recover, meaning that trying to do the minimum and safest actions with it since playing with code may be too risky.
I’d consider creating a new wallet (carefully saving the mnemonic) and simply transfer to the new one. Then, if you want, try to recover it.