On the back they are placed just above the seam where the tails are. The right tail overlaps the left one considerably and you could use that as a guide for placing the buttons.
Then there are two on each side of the front. Beginning with one in the lower corner a couple inches above the hem, and then placing the next one a couple inches up and out from it - to account for the angle of the lapels opening up.
Since the gold sequin fabric is notoriously delicate, I recommend sewing the button all the way through the the lining as well. And if you're missing any buttons from a coat I've made you just let me know and I'll ship you a replacement!
