All this is from memory, so forgive any minor errors, please. I haven't read a comic book in almost a decade now, because DC got too repetitive and silly, and I never could get into Marvel (although I do like the recent X-Men and FF movies.)
Golden Age: I don't believe it was ever addressed. It was taken as a given as we were introduced to Kal-L that he was a reporter at the Daily Star working for editor George Taylor, a job he apparently got after he moved to Metropolis when Eben and Sarah Kent (his foster parents) died. By the time he was later reintroduced as "the Superman of Earth-2", he had apparently moved on up to be editor, himself. Conclusion: Probably got the job through the Good Ole Boy network moreso than by resume, like a lot of things got done back then (and, unfortunately, even now, all too often.)
Silver Age: If I remember correctly, Silver Age Kal-El went did go to community college or some such, but didn't leave the farm until Jonathan Kent died - Martha lived a while longer. He had already enjoyed a considerable superhero career and was known all over the world as Superboy, though. He got the job at the Daily Planet by breaking the story of Superman coming to Metropolis, saving an airliner, and declaring that Metropolis was going to be his home and under his protection. Conclusion: Maybe he used super-hynotism to get the job :rollseyes: or maybe one of Baskin and Robbin's 37 flavors of Silver Age Kryptonite turned him into a world class journalist. Who knows, who cares?
Modern Age: Clark went to Smallville Community College for journalism, same as he will probably do on the tv series Smallville. He then went into Metropolis to try to make his way as a normal guy, and really wasn't having too much luck. He ended up saving a crashing airliner, and then briefly retreated to Smallville to rethink his approach to life. (Lois broke the story of a "Superman" who had saved the plane.) A costume was made based on the name Lois had christened him with, and he returned to Metropolis. He interviewed with the Daily Planet, and got the job based on getting the first interview with his alter ego. Conclusion: This version is probably the one who dealt with something most closely approaching reality for his employment, although not as tough as it is now - it was only the mid-to-late 80s, after all.