Can I use 888 fertilizer on cabbage & lettuce plants & do I just sprinkle on top of the dirt or work it in?

Its probably best to work it into the root zone. The general purpose fertilizer you are using won't burn the roots and some of the minerals in fertilizer move through the soil very slowly. I generally add this type when I am tilling the garden and it mixes it through the soil. For plants that are already established, just work it in a little around the plant.