On etherscan site you can find section "Token - View Tokens", then choose any popular ERC20 token (Bancor for example - #20), choose "Token holders" and you can see addresses which have the biggest amount of chosen token. This is one of way for detecting whales.
it is the same situation with all the altcoins that don't have fully anonymous transaction, which is practically 99% of them. you can always see their rich lists somewhere. for example
https://chainz.cryptoid.info/ has lists of most of the altcoins and their richest addresses.
and it is always the same, some exchange or some developer who owns the coin and its premine or ICO or something like that. it is rarely and nearly never an individual who actually bought and holds all of the coins in one place and becomes a whale. whales usually don't stay in one altcoin!