hi
I've installed the Nano wallet. Is it possible with this wallet to save the wallet.dat ?
There's no wallet.dat with Shift. You gain access to your wallet through your passphrase (ie your wallet IS your passphrase), either with the webwallet, the desktop wallet or by running a node. Fore more security, it is recommended to setup a second passphrase.
1st passphrase only => wallet access, send coins and vote.
1st + 2nd passphrase => 1st=wallet access, 2nd=send coins and vote