Complex sentence: A scientific journalist needs to be proficient in two areas: as a journalist, he must write well enough for magazines and newspapers, and as an amateur scientist, or at least as a dedicated learner capable of following complex science and explaining it in simple terms.
Split into simpler sentences: A scientific journalist needs to be proficient in both areas: as a journalist, writing good enough for magazines and newspapers. And as an amateur scientist, or at least as a dedicated learner capable of follow a potentially complex science and explain it in simple terms.