NftItem

TonSdk.Contracts.nft

NftItem is a class that contains method to work with transferring nft items.

It returns Cell in output and this cell can be setted like message body in Wallet.CreateTransferMessage .

You can find tutorials of message sending in one of the wallet topics.

To create nft transfer request, you can use NftItem.CreateTransferRequest :

// define the address of the nft collection
Address collection = new Address("/* nft collection address */");

// define index of the nft what will send
uint index = 10;

// get the nft items address using TonClient: TonSdk.Client
Address nftItemAddress = await tonclient.Nft.GetItemAddress(collection, index);

// create transfer options
NftTransferOptions options = new NftTransferOptions()
{
    NewOwner = new Address("/* receiver address */") // new nft owner address
};

// create a message body for the nft transfer
Cell nftTransfer = NftItem.CreateTransferRequest(options);

// create a transfer message for the wallet
ExternalInMessage message = wallet.CreateTransferMessage(new[]
{
    new WalletTransfer
    {
        Message = new InternalMessage(new()
        {
            Info = new IntMsgInfo(new()
            {
                Dest = nftItemAddress,
                Value = new Coins(0.1) // amount in TONs to send
            }),
            Body = nftTransfer
        }),
        Mode = 1
    }
}, seqno).Sign(mnemonic.Keys.PrivateKey);

// get message cell
Cell cell = message.Cell;

// send this message via TonClient,
// for example, await tonClient.SendBoc(cell);

You can find more NftTransferOptions here.