When using persistence via DynamoDb in an Alexa skill, the user structure is stored in a table with ID (key) and attributes (one field), which contains the complete user map as a flat string.
You can also see the notation of the substructure with name, type and value in the value of the string for attributes.
If you try to search via the aws console, you can only search for top level items. The idea was to use "contains" to find some sub-elements or values of the user structure, but the search does not return any results.
If you try the same in a specially defined table, it is possible to search in a string with "contains" and all elements that have the substring in value will be listed.
Is there something you need to further specify when searching?