At this very moment, there are no known exchanges you can buy Punk Vault (NFTX) (PUNK) on.
But because Punk Vault (NFTX) (PUNK) is an ERC20 token, you can use a decentralized exchange like Uniswap if the pair has any liquidity added to trade.
You can get the contract address of Punk Vault (NFTX) (PUNK) here.