Tokens that has already been listed in exchanges are mostly posted in Coinmarketcap. But there are also a lot of coins that are on exchanges but wasnt applied to coinmarketcap so what I do it visit the telegram and twitter account of the coin to see their announcements about where they are listed.
You're mistaken mate, only coins that have a minimum market volume of 100k within 24hrs will be listed on it. Some coins can be track by using BitUniverse apps which you can find there what exchanges that is currently listed. In other way also, by visiting their sites and telegram participation.If coin is not even on coinmarketcap or coingecko it is not the best idea to sell now
But who knows, maybe they will never be there.I think telegram is the best way to figure out exchanges where coin can be trade also.