How to transfer bitcoins from old wallet to new wallet? Have no wallet.dat info
If you were using the Bitcoin QT (aka Bitcoin Core) client, then the private keys you need are in the wallet.dat file.

If you can't get that file, and you don't have any other record of the private keys, I'm sorry to say your funds are lost.

If you had used the Electrum wallet instead, you could recover your keys using the 12 word "seed", if you had that.

There were other wallets in use too; if you think you used something else as a wallet, let us know.