To duplicate a layer in Figma it is very simple:
- Select your layer
- Hold CRTL or Command + C to copy the layer.
- Next, Past your layer with CRTL or Command + V.
If the source layer is contained within a frame or a group. The duplicated layer will be placed on top of the original layer when you paste it.
To make sure your layer is duplicated, go to the layer section and check the layers list for a duplicated layer.