Run libreoffice --writer to start LibreOffice Writer.

In this case, I guessed that it might be libreoffice or similar, so I entered libre in a terminal and pressed tab twice. libreoffice was one of the options, so I ran that. It started something from which one could choose to go to Writer, Calc, Impress, etc. Since you asked specifically about Writer, I looked at man libreoffice, which mentions -writer as one of the command line options. Running libreoffice -writer worked but resulted in

$ libreoffice -writer

Warning: -writer is deprecated.  Use --writer instead.

And so I got to libreoffice --writer.

In general, one could try things like the following:

• Guess and try names, based on the name of the application. Use Tab-completion for help. Read man pages for options.


• Run the program (using a GUI menu or however else you run it), guess the process name, and check using ps aux | grep guessed_name.


• If you know that the program belongs to installed package X, run dpkg -L X. It will list installed files from package X, look for /usr/bin, /bin, /sbin, etc in the output.



• One can find out the process corresponding to a window as follows :

  
  
  

  Run xprop _NET_WM_PID, navigate to the target window (without clicking!), and click on it. This will print the PID corresponding to the window, for example

  
  
  

  _NET_WM_PID(CARDINAL) = 7394
  
  

  
  
  

  Now run ps -p 7394 (with 7394 replaced by the PID you got) to find out the process name for the given PID.