lnovoa - thank you for your fast reply.
While I was working on my answer I discovered that things are now working as expected - I swear that I did nothing more than restarting my computer
The difference may be that I am using now a star (*) to make the search term more general. So - my original question is answered now, I understood how to set references to internal documents, folders, dashboard Wiki pages, and external URLs.
A big thank you to the whole OpenKM team!
Here is my intended answer:
My use case is the organization of scientific publications. My top categories are journals, books, thesis, presentations, brochures, and more. I created directories for each top category with the same name. In journals 36 subdirectories are created (A - Z and 0 - 1). For each journal (e. g. Journal of Fluid Mechanics) another subdirectory with the journal name exits which are sorted in one of the 36 directories according to its first letter in the journal name. Any paper of this journal is stored in the journal directory.
I want to use the Wiki extension to store meta information like general information about the journal (ISSN, open access, etc.) or some remarks about a specific publication. It would be useful to link to other documents, Wiki pages, or directories, in the Wiki entry. There are buttons in the Wiki editor to add documents, folders, other Wiki pages, etc. By clicking on of these buttons I get a dialogue box with a possibility to enter a text but nothing happens - no documents or folders are showing up. However, I can manually add entries using the respective UUID (e .g folder: [fld=UUID]Name[/fld].