I recommend to choose a cryptocurrency exchange which is safe, this is the most important for every trader! Try one of the platforms which have great opinions among traders, for example CoinDeal or Kraken. These two are my favourites, but now I can especially recommend CoinDeal because of its attractive fees and free deposits. It even has the VQF Swiss License so it's super safe. Here you've got the link:
https://coindeal.com/.
He can choose Binance, Kraken, Kucoin, Bittrex, and I think that exchanges have a big exchange. He can find so many coins listed on that exchanges so he can start trading without any longer. But if he cares about his document or he doesn't want to send any document to the exchanges, he can choose Binance as we know that in Binance, we are free not to send the document, but we have a limit amount in withdrawal. I guess that will not be a problem for him if he still needs to learn more about trading.