You can't know if a coin is in a cold wallet or in a hot wallet, only the owner knows it, from the outside view it's the same. What we can know is the rough estimate of coins in wallets of big exchanges like Coinbase, and we can assume that majority of those coins are actively traded, but even here some percentage of users actually use exchange accounts for long-term storage, even though it's a bad idea. Coins in self-hosted wallets could also be actively traded, this can be spotted if they are moved frequently.
If I were to calculate an estimate for the circulating supply, I would look at all UTXO and consider all coins that haven't been moved in last 2 years as non-circulating, except for coins that belong to exchanges.