You would need to breed a female Lucario and a compatible male Pokemon who knows Bullet Punch. Up until Gen VI, the only Pokemon who could fit this criteria by learning the move through level-up was Hitmonchan, however Pangoro can learn Bullet Punch through level-up in Gen VII. Those are the easiest ways to obtain a compatible Pokemon, although you could also use a Smeargle, who learns it through Sketch.
The resulting offspring should be a Riolu with Bullet Punch.
Hope I helped. :)
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