I moved one of my downloaded torrent files and now ktorrent can't find it. That's not surprising -- but how do I clue ktorrent in as to what its current location (on my machine) is? ktorrent's file list shows the previous location but offers no way I can see to modify that information.

open it from ktorrent or adjust download location in settings

I already changed the download location, but the file that produces the complaint, which actually is in the download location, is one that existed previously in a different location. That previous location, not the download location, shows up in the ktorrent file list. In other words, changing the download location takes care of the future but not the past.

I also tried opening the file from ktorrent (File / Open) but when I pointed ktorrent to it, I just got a blank window that I couldn't open. Is there some other way to open it?

The file list has the message "Error: Data file is missing" even though the file in question is in the download directory.

I discovered the solution: when ktorrent starts up, it complains if it can't find one of the download images it's looking for. At that point there's a choice of specifying a different location, and then you can indicate where the download image currently is. (If you want to do this when ktorrent is already running, stop and restart it.)