Ctrl+Click on the node you wish to copy and drag the copy to its desired location. Connections to source nodes will be replicated, but connections to nodes which come after the copied node will not. You may also:
- Right-click the node, and then Copy and Paste.
- Use the Edit > Copy or Paste feature in the toolbar, after selecting the node.
- Use the keyboard shortcut: Control + C to copy and Control + V to paste.