There is no QDLS library. The documents and folders in the QDLS file system are actually stored in QDOC library. You can list all of these folders and documents (object types of *FLR and *DOC) using the WRKDOC command. If you just display QDOC library you will not recognize the document names as the iSeries assigns a dummy name to them.
If you are working within a CL program, you can use the QRYDOCLIB command to build an output file of all documents or specific documents. The command has filtering for various bits of data such as user creating the document, create date, folder to search etc. The data in here will list the iSeries assigned name of the document but also the PC formatted name of the file.
Hope this helps.