Which component CANNOT be co-located with Delivery Controller on the same server?

SQL Server can be co-located on the same server as the Delivery Controller and is a supported configuration, though Citrix recommends a dedicated SQL Server instance for production environments.

The Citrix License Server is supported for installation on the same server as the Delivery Controller, making co-location a valid and documented configuration.

StoreFront can be installed on the same server as the Delivery Controller, as this is a supported configuration documented by Citrix for smaller or proof-of-concept deployments.

Citrix's system requirements documentation states that the Delivery Controller must not be installed on a server running the Domain Controller role, because the security model and service interactions between Active Directory and Delivery Controller components create conflicts that are not supported. All other listed components - SQL Server, License Server, and StoreFront - are permitted for co-location with the Delivery Controller, though dedicated infrastructure is recommended for production deployments.