I see that you are looking for a quick way to clone issues in Jira. While there is not a single key keyboard shortcut for this action, there are some steps you can take to do this quickly from just the keyboard.
When you are viewing an issue directly or on a board, you can press the . key first. This will bring up an actions menu (if you have keyboard shortcuts enabled). From there you will need to start typing out the word "Clone". You can then press enter to bring up the clone dialog box which will ask what the name of the issue should be and whether or not to clone attachments.
In my testing this was about 4 keystrokes to do in both Jira cloud and Jira server.
Does this help?
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