If you have several ETH addresses and you don't remember which one contains the DOT tokens, you have several options to find out which one is the right one: 

Enter your Ethereum address in step 1 on our claims page here and you will be shown whether it contains claimable tokens or not.

You can also enter your address in the search field on etherscan.io to see which tokens it contains (if it doesn’t contain any tokens, the Token field will not be visible). You're looking for "DOT Allocation Tokens":