vnet_subnet_id

PS C:\> $myResourceGroup = "MPN-Pool1"
PS C:\> az network vnet subnet list --resource-group $myResourceGroup --vnet-name azdmz1

[
  {
    "addressPrefix": "172.30.1.0/24",
    "addressPrefixes": null,
    "delegations": [],
    "etag": "*****",
    "id": "/subscriptions/*****/resourceGroups/MPN-Pool1/providers/Microsoft.Network/virtualNetworks/azdmz1/subnets/default",
    "ipConfigurationProfiles": null,
    "ipConfigurations": [
      {
        *****
      }
    ],
    ****
  }
]
PS C:\>