The generic function dde-server-topics returns a list of the available general topics on a given server. A suitable method specializing on the server class should be defined. Dispatching topics (see define-dde-dispatch-topic) should not be returned, as they are handled automatically by LispWorks. If you do not provide a dde-server-topics method, the default method returns :unknown, which prevents the DDE server from responding to the topics request.
Generally only one canonical name should be returned for each topic, even though the server may recognize several alternative forms of name for a topic. For example, if an application implements a topic for each open file, the topics foo, foo.doc and c:\foo.doc may all be acceptable strings for referring to the same topic; however dde-server-topics should return each topic once only.
The application must also provide a method on the dde-server-topic generic function.
LispWorks User Guide and Reference Manual - 20 Sep 2017