what is the minimum trade volume to qualify for a trading competition and become one of the champion
You just need to generate €500 worth of trading volume, and deposit €100. In July. You will then be in the raffle to win €500 (5 winners, so €100 each!).
Fees are superlow so you could just deposit, buy and sell Bitcoin a few times, (0% maker fee) and then you'll qualify.
But CoinMetro has a lot more to offer so it's a great place to stay and trade in the future. 0% maker, 0.1% taker, EUR/GBP etc.