The Project References menu item appears in the Project Properties dialog for EventFlow and LiveView projects as it does for all Eclipse project types. It is possible to specify a project reference with this panel, but that reference is ignored by Studio.
To make available the modules and resource files in another project from the current project, you must add the referenced project as a Maven dependency of the referencing project. For example, to reference files in EventFlow project B from project A, you must add a Maven dependency on B from A.
Use > from the right-click context menu of project A to add project B, or edit project A's pom.xml file, and use the POM Editor's Dependency tab.