After Effectsでレイヤーを複製する方法

You can duplicate a layer by selecting it and pressing Ctrl+D (⌘+D).
You can do the same by selecting a layer and pressing Edit – Duplicate.

How to duplicate multiple layers?

You can duplicate multiple layers at once. Make sure to select multiple layers holding Ctrl or Shift (⌘ or Shift) and pressing Ctrl+D (⌘+D).