As the previous poster indicated, you need to read the batting package info to see the largest area you can leave unquilted. I would think about a quilting path that will allow you to quilt edge to edge. So a line that goes from one side to the other across the bottom of the focus squares and another that goes along the top. You could also do one that goes along the seam between the shadow & the background. Then the same spacing up and down. This is assuming your batting allows the focus squares to remain unquilted. You don't want to quilt around the perimeter of each square. This would make you have to turn your quilt which may be cumbersome (depending on your machine), and you would have a bunch of starts and stops requiring tie offs and/or burying the thread tails. Another option would be all over diagonal lines disregarding any piecing seams. A nice classic pattern.