Grammy's book of Voodoo is sitting on the piano at Donut Hole Billy's.
You really should ask Billy before you take it. Ask Billy about the book to get it.
Unlike normal walkthroughs, in Nice Game Hints you can select just the puzzle you want hints for. Here are listed the puzzles for "Grammy's Book of Voodoo" in Voodoo Detective. The guide you choose only contains information about that puzzle, reducing possible spoilers for other puzzles.