There are several places where this can be accomplished:
Go to https://counterwallet.io and look under Exchange.
Your own assets are displayed under My Balances (in each address).
Some other sites display a smaller selection of Counterparty-listed assets/tokens, e.g. coinmarketcap.com and other.
Not every asset is what it seems. Watch out for fraudulent assets and do your own diligence. Anyone can create an asset/token in a decentralized manner.