I will open accounts on some exchanges soon. I would like to prioritize one where I will be able to practice for free. From what I have read and seen so far, Binance seems to be considered the best exchange overall. However, I didn't see any mention of being able to practice for free on Binance website. So which exchanges would be best for that?
I still don't know what kind of deal you're talking about. But for normal trading, exchange doesn't seem to support it. because it is one of those transactions that is easy to understand. As for margin trading, there seems to be a lot of support exchanges. You can access and try demo accounts at Bitmex, Snapex, Bingbon. There you can freely demo transactions with huge accounts.
I suggest trying with Bitmex testnet to practice as many of us suggest the same website. I think that will better to him to practice his skills and he can improve from that trading before he enters the market with his money. Perhaps, he wants to know and learn about how to analyze the coin movement, how to analyze the chart.
But I don't suggest to try margin trading as he should have enough skills to trade. Margin trading will be more complicated than the usual trading at the exchanges because you use the money from the exchanges to trade. If you make a profit, then your profit will be bigger, but if you lose, your loss will be bigger too.