To get the egg move on Absol, you must breed a female Absol with a male Sawsbuck (in your case*) that knows MegaHorn. The baby should be a Mega Horn Absol. The original Absol will not know the move. I hope this helped. Welcome to the site. Comment if you have and further confusion regarding this.
*Other possible parents (must be male and have learned Mega Horn) : nidoking, rapidash, rhyorn/rhydon/rhyperior, Samurott, or Bouffalant (or an absol that already had the move bred onto it)