Yobit - does around 32m in daily volume and roughly 1900 markets?
Kucoin - is a great exchange eager to get new listings with lots of bounties!
OKEX - is #1 in volume with 500+ markets
Any exchange with KRW tradings pairs is going to see plenty of daily volume
OKEX volume is completely faked, Kucoin is likely padded as well but nowhere near as much as OKEX, Binance, CoinEgg, or any of the other Chinese exchanges.
Trex, Qryptos are gtg and IDEX, Crypto-Bridge, or some other DEX is what should be focused on. The masses will migrate to DEX when they understand the volumes are faked.
Here is a good starter:
https://medium.com/@sylvainartplayribes/chasing-fake-volume-a-crypto-plague-ea1a3c1e0b5e