BNB token address is the address associated with your BNB wallet. To find the address, you first need to get on the BSC (Binance Smart Chain), create a wallet, back the same up using the seed phrase, eventually click on the "Smart Chain' tab, and get the BSC address. For the exchange wallet, you need to select the deposit option, choose BNB as the preferred crypto, and the Binance Smart Chain as the network. That way you get the BNB token address.