I'm assuming you only "see" 4 abdominal muscles visible (4-pack). The easiest way to get all your abdominals showing is to reduce your body fat to under 10%. Even if you don't have strong abdominals they will be showing.

The other reason but much less likely is that you don't train your lower abdominals. V-Situps are great, leg lifts, ab roller extensions.

Nothing comes fast without cons. Slow and steady and you will see results.
Sorry what i meant with fast is atleast 6 months to get a six pack
I am thin(55kg) so i think a diet isnt that good for me but I try to eat something with carb. as less as possible and eat more protein like chicken,fish and more vegetables than usual.
I do the v-sit ups and and leg lifts but im gonna try the ab roller extension

I need a training plan(for abs) pls because my body is getting used to the training method and pattern that i know and it wont be a challenge for my body anymore.