You can create a Requirements Diagram for sub-requirements of the selected requirement directly on the diagram pane.
To create Requirements Diagram for sub-requirements
Select a Requirement shape on the diagram pane.
On the smart manipulator, click the Create diagram for sub-requirements button.
A new requirements diagram for the sub-requirements is created having the same name as the selected requirement. The selected requirement is an owner of sub-requirements diagram and is marked with the diagram sign.
Double click the owner symbol to open a diagram for sub-requirements and use navigation buttons on the diagram toolbar to move back or forward through diagrams.