I'm 16 and a guy how come when i jump i see my muscles better, my body jiggles but i see my v-cut muscle i see my abs but that's it why is that?

Flexing/stretching: It sounds like the action that you take when you jump stretches/lengthens your core and flexes the muscles in a way that makes them more visible than normal. As it would be weird to go around jumping and shirtless, I would suggest that you like the body you have and continue to strength train if you wish to have abdominal muscles that are more visible at other times.