To create a com.nomagic.magicdraw.uml.symbols.paths.PathElement for given ModelLink between given client and supplier elements, use method com.nomagic.magicdraw.openapi.uml.PresentationElementsManager.createPathElement(Element, PresentationElement, PresentationElement):
The diagram is not passed into createPathElement(Element, PresentationElement, PresentationElement) method. A new path element is created in the same diagram as client or supplier presentation elements.