Trying to understand how bitcore-node stores the data in the DB
Bitpay's bitcore-node project uses the same datadirectory as Bitcoin Core. You can see this in their sample configuration in their README:

var configuration = {
    datadir: '~/.bitcoin',
    network: 'testnet'
};


As such, the you can see: What are the keys used in the blockchain levelDB (ie what are the key:value pairs)? for information on what is in this database. However, bitcore-node does provide another interface for storing extra data about addresses and their balances. This is defined in this file. You have to enable this in your configuration and re-index the blockchain to enable this module, as their README details.

As these lines show, for each output, key-value pairs are added to the leveldb database in this format:

key:   [AddressModule.PREFIXES.OUTPUTS, address, timestamp, txid, outputIndex].join('-'),
value: [output.satoshis, script, height].join(':')


And, similarly for inputs, this is the format of the key-value pairs:

key: [AddressModule.PREFIXES.SPENTS, input.prevTxId, input.outputIndex].join('-'),
value: [txid, j].join(':')