ninjask dosent evolve
Nincada evolves into Ninjask at Level 20.
Ninjask cannot evolve any further. If you are meaning Nincada, it can evolve into Ninjask at level 20, but it can also evolve into Shedinja, if you have an empty party slot and a Pokeball with you.
You can only get Shedinja if you have and extra space in your party and an extra pokeball when Nincada evolves into Ninjask. It is a "special" or "castoff" evolution.
Level 20.
No Ninjask cannot evolve but Nincada evolves into Ninjask at level 20 but if you have a poke ball and a empty slot the empty slot will be a shedninja
ninjask doesn't evolve but if you have a empty slot of your Pokemon team when nincada evolves to ninjask a shedinja will appear in the empty slot.
level 20 (ninjask)
Nincada evolves into Ninjask at level 20 while Nincada evolves into Shedinja when you level it up while you have space in your party and your belt.
Trapinch learns Dig at level 41, but only if you do NOT allow it to evolve into Vibrava. Nincada learns Dig at level 45, but only if you do NOT allow it to evolve into Ninjask.
Ninjask is the highest evolved form, thus meaning he cannot evolve any higher. But it is possible to get two different Pokemon from evolving his pre-evolve form Nincada. Simply Evolve Nincada into Ninjask with an open slot inside your party and you will get Shedinja.
Ninjask doesn't evolve.
The only way to get NINJASK is to get a nincada near rubusto city and evolve it!