You can check the wallets of the top exchanges like Binance, Huobi, Bittrex, Upbit and Bithumb.

Some of them:

bittrex
huobi-withdrawal
huobi-pro
user.dunamu

Also this weekly report from the penguin :)
@penguinpablo/weekly-report-how-much-hive-is-stored-on-the-exchanges-december-16-2020