This displays your bookmark (that you have to populate with for instance keditbookmarks).
You can browse them and click them to open.
You also have the possibility to add okular bookmark to it.
It needs a c++ backend. So you will have to pull the source from github and compile.
The compilation process is standardr (mkdir -p build && cd ./build && cmake .. -DCMAKE_INSTALL_PREFIX=/usr && make && sudo make instlal)