to reproduce the command killed with ctrl+u
 

The command entered on the commandline can be erased using ctrl+u.Then which is the shortcut key to reproduce the command which was killed..?

Killed? Erased from the current command line. There is no control sequence to rewrite the command line, unless you've copied it in the buffer, so you can use the middle mouse button to paste. Just be patient and rewrite the command line from the beginning! ;)

If you've prev used the same or similar cmd, try the history cmd.