A cub is a baby animal such as a lion or a wolf. A cub reporter is a young or inexperienced reporter. I have never heard 'cub' used as a verb in this manner, but from context I suspect it means to dig or search for something.

I've never heard this usage. I do not know any verb "to cub" and neither does ahdictionary.com. Can you quote more of the passage? I think it's possible that there's a transcription error. WARNING, WILD GUESS AHEAD. In English it is sometimes possible to use a noun as a verb. For example, I know of a lawyer who advertises "Sensitive lawyering at sensible prices," and one can say "In my college years I waitressed during the summer." "To cub" might mean "to work as a cub reporter." If so, the sentence might meaning something like this: "Cub reporters get paid almost nothing. If you ask them "why do you cub," the answer is always the same. They cub for the opportunity to get experience in reporting."