Can't tell from the pics but it looks like there may be a spot in the dorsal fin which would indicate female. If there is not a spot in the top fin then you're going to have to grow it out a little first and take some pictures of the vent area for us.
Why not buy it a mate from the same place you got this one? You're probably better off not trying to breed it right away if this is your first time keeping flowerhorns. What size tank does he/she reside in at the moment? Any tank mates?