See the C-GET Operation definition for the Query/Retrieve Service Class (C.4.3). No Extended Behavior or Relational-Retrieve is defined for the Hanging Protocol Query/Retrieve Service Class.
Query/Retrieve Level (0008,0052) is not relevant to the Hanging Protocol Query/Retrieve Service Class, and therefore shall not be present in the Identifier. The only Unique Key Attribute of the Identifier shall be SOP Instance UID (0008,0018). The SCU shall supply one UID or a list of UIDs.
Note: More than one entity may be retrieved, using List of UID matching.