Copying and pasting annotations from one item to another can be accomplished by using the options in the right-click context menu inside the player.
Right click on the item from which you'd like to copy annotations, and choose the Copy Annotations option from the menu.
Next, right click on the item that you'd like to paste those annotations on and choose the Paste Annotations option from the menu.
The Paste annotations dialog will appear, allowing you to choose if you'd like to paste Comments, Sketches, or both to this item. You also have the option to set the start frame for these annotations, in case you need to offset them from the original item. When you're ready, click Paste to complete the operation.