There are two ways to prove that Craig is Satoshi.

1. Satoshi must have access to the private keys of the earliest bitcoins that was mined and stored in a series of addresses that hold 50 bitcoins each. These bitcoins were never moved since then. If Craig is Satoshi, he must have access to these wallets and he can simply move a small amount from one of these addresses to a different address. Pretty simple!

2. Mark the below address. This adress holds the bitcoin's first ever mining reward which we call "genesis block".

12c6DSiU4Rq3P4ZxziKxzrL5LmMBrzjrJX

Real Satoshi must have access to the private key of this wallet and he can simply sign a message to prove his real identity. If Craig can do it, we will undoubtedly call him as Satoshi Nakamoto.

But Craig couldn't do any of these till date. So no one really believes his claim. The Binance CEO wrote about this already. See the link below,

https://coingape.com/how-prove-identity-satoshi-nakamoto-cz-suggests/

Hope this answers your question!