Adding reference projects to a standard project is a property that the Administrator can set in Talend Administration Center. For further information, see Talend Administration Center User Guide.
Once the connection between the projects is established, you can launch the Studio and open the main project in the Profiling perspective and share all items from the reference project (connections, patterns, indicators, rules and so on). All items in the reference project(s) will by default show in the DQ Repository tree view either as a separate reference project preceded by the @ sign, or as separate items preceded by the @ sign as shown in the below captures respectively:
Note that reference projects may contains analyses and reports, but you can not modify them from the current project. All items from a reference project are read-only.
For further information about using reference projects, see Working with referenced projects.