DynamoDB (and other dynamo-like systems like Cassandra, Bigtable) are just advanced key/value stores. They support multiple levels of keys->values but fundamentally you need the key to find the associated value.

If you want to search by parameters that aren't keys then you need to store your data that way. Most of these systems have secondary indexes now, and that's basically what they do for you automatically in the backend, storing another copy of your records using a different key.

If you need adhoc relational queries then you should use a relational database.