1. How can I generate a transaction without private key?
I don't know whether it's possible with TITAN. If it's not and I choose to compromise the anonymity, how can I generate the raw transaction on an online machine?
with TITAN each unspend output has a seperate private key that can be derived from the master private key of your account. You will not be able to sign any transactions if you do not have the corresponding privkey of the unspent outputs.
However, you do not necessarily need the master private key .. but I am not sure if it is wise to work on derived private keys (and possibly expose them) as there are some security issues with ECC concerning derived private keys .. best practice would be to let the wallet handle derived priv keys..
Or are you talking about unsigned raw transactions .. that should be possible with titan .. but currently is not yet implemented.
2. How can I sign it on an offline machine?
TITAN is based on ECC as is bitcoin .. I don't know about the explicit transaction structure but I am very sure something like 'offline' signing is possible and will be implemented in future .
Further .. BM once stated that he has some nice ideas about some observer-keys that can only do read-only .. (ECC magic)