Question is in the title? What dungeon do i complete for these tokens? Am i just being stupid and not seeing what might be obvious?
I think you can obtain them by completing any of the dungeons... Well I only tried it with Tiamat sides since that was the only dungeon I could play on my Violet.
I got tokens from guro sector missions. I think the tokens can be stored in acct bank as well, so have at it. (should problem confirm that for yourself just to make sure)
Like most events, completing any dungeon (exc. special ops and maybe training program) will grant you a token, so do whatever you like.