...whatever happened to Superman's clone?
The answer to that question happened in Action Comics #524 (October, 1981) by Martin Pasko, Curt Swan and Frank Chiaramonte...
...with the confrontation dramatized on the cover by Ross Andru and Dick Giordano.
If I Can't Be Clark Kent....Nobody Can
After a time, the clone woke up, thinking he was still Superman (but powerless), and used a Superman robot to get back to civilization. While there, working as Clark Kent (while Superman was in space), Perry White assigned him a story on now missing on a flight WGBS reporter Dan Reed and Superman Pavilion founder, J. Robert Arngrim. In researching Arngrim (and Luthor's clone plan), the faux Clark Kent started having some memories, fueled by the return of Superman to the Daily Planet. The clone hid, figuring out what to do.
One of the odder times Clark Kent battled Superman, but not the only time, as this shows. Plus, the second story of the issue features a battle between the Calculator and Atom and Air Wave!