From my last flight I know the answer:
They have indeed two versions of the A340-600. Exact same number of seats - however one version starting with windows (5A/5K) and the other version starting with (5H/J). In this later version they have consequently less of the of favourite window seats.
Therefore your 8K is definitely a window. However they are also sometimes changing the version and re-allocating seats. You can check a day before departure with a test-booking and look at seatmap. Afterwards changes are unlikely.
I had reserved 5A and during online check in was given automatically 6A (due to the change of a/c version). I.e. no problem for me but could have been if I would have had the window in the last row. Don't know what they do then ... probably you end up in some center or aisle seat.
Therefore I recommend to check in as early as possible and if it is messed up call the airport supervisor.