Welcome to Steemit,whales are people who have high Steem Power,let me hope you know what Steem Power means!
The best way to know these whaless is by seeing the trending page,most of those guys on the that page are whales.
Check out this https://steemit.com/trending
You can also check the hot page at certain time intervals or such specific tags/topics that interest you and comment on them.
Thank you!