When does Lucario learn dark pulse in Pokemon diamond?

, my name is Trixter, and I'm here to answer that question for you. Lucario never learns Dark Pulse on its own. You can however teach Lucario the TM, Dark Pulse.

Um no Trixter he doesn't have to use the TM and I suggest you don't waste it. What you should do is get a heart scale and go to the move relearner at pastoria city and he will let Lucario learn Dark Pulse.