You cannot. DynamoDB requires that all attributes you are filtering for have an index.

As you want to query independently of your main index, you are limited to Global Secondary Indexes.

The documentation lists on what kind of attributes indexes are supported:

The index key attributes can consist of any top-level String, Number, or Binary attributes from the base table; other scalar types, document types, and set types are not allowed.

Your type would be an array of Strings. So this query operation isn't supported by DynamoDB at this time.

You might want to consider other NoSQL document based databases which are more flexible like MongoDB Atlas, if you need this kind of querying functionality.

You can decode the values recursively with a well crafted function. It looks like the key names correspond to a type:

S -> string
N -> number
M -> map

Handle each of the cases you want to decode if possible, otherwise filter it out. You can make use of the various type filters and the alternative operator to do so.

$ cat input.json
{
  "Count": 1,
  "Items": [
    {
      "Id": { "S": "app1" },
      "Parameters": {
        "M": {
          "nfs#IP": { "S": "192.17.0.13" },
          "maxCount": { "N": "1" },
          "nfs#defaultPath": { "S": "/mnt/ebs/" }
        }
      }
    }
  ],
  "ScannedCount": 1,
  "ConsumedCapacity": null
}

$ cat ~/.jq
def decode_ddb:
    def _sprop($key): select(keys == [$key])[$key];                 # single property objects only
       ((objects | { value: _sprop("S") })                          # string (from string)
    // (objects | { value: _sprop("NULL") | null })                 # null (from boolean)
    // (objects | { value: _sprop("B") })                           # blob (from string)
    // (objects | { value: _sprop("N") | tonumber })                # number (from string)
    // (objects | { value: _sprop("BOOL") })                        # boolean (from boolean)
    // (objects | { value: _sprop("M") | map_values(decode_ddb) })  # map (from object)
    // (objects | { value: _sprop("L") | map(decode_ddb) })         # list (from encoded array)
    // (objects | { value: _sprop("SS") })                          # string set (from string array)
    // (objects | { value: _sprop("NS") | map(tonumber) })          # number set (from string array)
    // (objects | { value: _sprop("BS") })                          # blob set (from string array)
    // (objects | { value: map_values(decode_ddb) })                # all other non-conforming objects
    // (arrays | { value: map(decode_ddb) })                        # all other non-conforming arrays
    // { value: . }).value                                          # everything else
    ;

$ jq 'decode_ddb' input.json
{
  "Count": 1,
  "Items": [
    {
      "Id": "app1",
      "Parameters": {
        "nfs#IP": "192.17.0.13",
        "maxCount": 1,
        "nfs#defaultPath": "/mnt/ebs/"
      }
    }
  ],
  "ScannedCount": 1,
  "ConsumedCapacity": null
}

After looking through documentation it is not feasible to implement the search fields as I originally intended. The problem is that while the values are JSON they are stored as string literals so I have to do refactoring to start storing as JSON objects. Additionally I cannot add in columns and index because the search could operate on any number of fields and different items can have different fields, i.e. an Item can have Brand, BatteryInformation, Name. Given that the requirement is that any of these subfields should be searchable its better to do this in Cloud Search or ElasticSearch where I can index and search on arbitrary fields and values within a column of an object.

Since this is a DynamoDB table, I am going to use CloudSearch since it offers easier indexing option and integration for data.