The 3 Keys to Fat Loss.
Plus, you can't spot reduce fat through exercise.
As to what body composition you are to see your abs, that will change from individual to individual, as sex, height, muscle mass, and genetics all come into play here.
As far as doing abs at home to build them up, there are plenty of things that you can do. Just select a few exercises (i.e. crunches, weighted crunches, double-leg raises, v-sits, deadbugs, etc.) and do them. Otherwise, make sure that you are doing core exercises in your resistance training sessions.