A Pokemon can evolve at LV 100 if it evolves through an elemental stone(Water Stone, Fire Stone etc..). If it is through LV, then no it cant. For example, you raise a Voltorb to LV 100, but you can't evolve it anymore no matter what you do. A Pokemon cant evolve by itself if it needs a stone, you need to give it the stone to evolve it. Trading works the same way as Stones, you can evolve it if it evolves with Trading with or without an item.