The easiest is Chapter 1 boss. Double jump above his head and press D-pad Down, X Button. Now keeping hold down D-pad Down and keep pressing X Button. He may jump around which will hit you and break your combo. Just start again and you should get it. It's easier if you have another player distracting him.
Another easy way is jumping on a stack of Bone Pillars, which can be found in Chapter 2. Depending on your damage, you can get about 10 hits on each head.
Tip from XainTheGreat:
Jump kicking on an partner's head 30 times in a row will unlock this trophy as well.
If you have a friend or can get online you can get this trophy on the first chapter with out even moving. just ask the second player to stand still and jump kick his face until you get your trophy.
Sourced: All Credit goes to Original Authors.http://www.playstationtrophies.org/game/castlevania-harmony-...