The GENESIS_JSON file is referenced in the env file:
GENESIS_JSON="${CNODE_HOME}/files/genesis.json"
This file looks to be correct for testnet:
cat ${CNODE_HOME}/files/genesis.json
{
  "activeSlotsCoeff": 0.05,
  "protocolParams": {
    "protocolVersion": {
      "minor": 0,
      "major": 2
    },
    "decentralisationParam": 1,
    "eMax": 18,
    "extraEntropy": {
      "tag": "NeutralNonce"
    },
    "maxTxSize": 16384,
    "maxBlockBodySize": 65536,
    "maxBlockHeaderSize": 1100,
    "minFeeA": 44,
    "minFeeB": 155381,
    "minUTxOValue": 1000000,
    "poolDeposit": 500000000,
    "minPoolCost": 340000000,
    "keyDeposit": 2000000,
    "nOpt": 150,
    "rho": 0.003,
    "tau": 0.20,
    "a0": 0.3
  },
  "genDelegs": {
    "2f56e87d67b8e5216582cfeb95dbdc9083110a3ef68faaa51bef3a80": {
      "delegate": "bd5933d3c5417f17a64c7214711a26abc3bc03e2c90dc1bb38e0c39f",
      "vrf": "9a0b0f537874d089cedfa9e250150405e47ea29acee87c40a223ae0a175d26f8"
    },
    "514e81afb082fce01678809eebd90eda4f7918354ec7d0433ad16274": {
      "delegate": "eff1b5b26e65b791d6f236c7c0264012bd1696759d22bdb4dd0f6f56",
      "vrf": "e6f70fb10c7523aa76648e20d17e65fd9b2ed53960fbd20b308f223b703f2e23"
    },
    "2fca486b4d8f1a0432f5bf18ef473ee4294c795a1a32e3132bc6b90f": {
      "delegate": "de665a71064706f946030505eae950583f08c316f0f58997961092b1",
      "vrf": "c3fde629add60e30142cd7ef3c680610975208b08aee42203a5c40ad5992e8f6"
    },
    "4ee98623920698b77c1c7f77288cbdac5f9011ff8970b1f507567d0d": {
      "delegate": "bf07107c6f632de95e34af7e009d2aafa19916c7ba89b944fbedcd72",
      "vrf": "9d7d12e3d6b02835be3e76cfc6ae93d937035ee0e006d04a0eef9dea19754e21"
    },
    "0d06d2547ed371fdf95fb5c4c735eecdd53e6a5bb831561bd0fcfd3d": {
      "delegate": "6df3e1b4b8a84c63c805076a85e5aa00924997a4eae85fddf0aee3ca",
      "vrf": "0774e5810fe02a014ec97ef424797172f2b8c5dcfb6e4cfc98b411c31d5096d8"
    },
    "581e23030b6038bae716e5d64b9e053db10541b12e6b0b4eff485454": {
      "delegate": "b0dca078b823cde627da136200d6618c49ad712b77972a1c5e135763",
      "vrf": "16a4e883b72ddbd09a4f8a1170fc346ab11e4202f814faa73e9d2433ee03e7b0"
    },
    "e5f27655371b54aed91cc916b2569060978be80056768fee2cc5ce1b": {
      "delegate": "b3873a254459f506e47b9a252ee7912e538b364447f31576a170db65",
      "vrf": "cc5c897fdf5db0017326656fe35aeb20c72b175540793f9b9b8dc9ade001bbc4"
    }
  },
  "updateQuorum": 5,
  "networkId": "Testnet",
  "initialFunds": {},
  "maxLovelaceSupply": 45000000000000000,
  "networkMagic": 1097911063,
  "epochLength": 432000,
  "systemStart": "2019-07-24T20:20:16Z",
  "slotsPerKESPeriod": 129600,
  "slotLength": 1,
  "maxKESEvolutions": 62,
  "securityParam": 2160
}