Kosher salt, in this context, refers to a coarse ground salt. For topping this vegan and gluten free pineapple banana bread you don't want to use finer ground table salt. Kosher salt, coarse salt, coarse sea salt, or coarse Himalayan Pink salt will all work for this purpose. Just use whatever you already have. The coarser grind allows the salt to sit on top of the bread more than just soak into the dough. This gives a greater flavor for the overall loaf.