Binance,bittrex,kucoin and other top listed exchanger will be good to buy digital currency.10k$ is huge money so before investment try to make a analysis where and which coin you should invest.
Is it true that a friend recommended me to buy digital currency for transaction on SunCoin platform and only need to pay a deposit to operate? Because this is my first contact
if you mean that thesuncoin.io then Suncoin website is unavailable now.maybe they are working on this site that's why site is off-line.you can see thesuncoin.io website don't have SSL certificate so this site is not recommended.
Or if you are talking about Suncoin (crypto coin) which already scam or deam and coinmarketcap already delisted it. you can check it here
https://coinmarketcap.com/currencies/suncoin/