I am using classic builder for template in my integration using SOAP API, Now Exact target launch new Content Builder functionality, Is it possible to retrieve the Content Items (HTML EMAIL) In Content builder folder using SOAP API.
No, you need to use the REST API.
Content Builder uses a separate data store for its content, and this has a new API. Unfortunately this also means you can't send a Content Builder email via the SOAP API without rendering it into a HTML template first and sending it the classic way.
The call you need is
You cannot use SOAP API on Content builder, only the REST API.
The SOAP API will only interact with items on the Classic version. Content Builder is hosted in a different location and will only allow REST API interaction.