You can quickly duplicate objects, groups, and entire layers by using the Layers panel.
Choose Duplicate “Layer name” from the Layers panel menu.
Drag the item in the Layers panel to the New Layer
button at
the bottom of the panel.
Start to drag the item to a new position in the Layers panel, and then hold down Alt (Windows) or Option (Mac OS). Release the mouse button when the indicator is in the position where you want to place the duplicated item. If you release the mouse button when the indicator is pointing to a layer or group, the duplicated item is added to the top of the layer or group. If you release the mouse button when the indicator is between items, the duplicated item will be added in the specified position.