Complex sentence: Nietzsche studied the work of Theognis during his university days at Leipzig and his first published article (in an influential classical journal, "Rheinisches Museum") concerned the historical transmission of the collected verses.
Split into simpler sentences: Nietzsche studied the work of Theognis during his university days at Leipzig. His first published article (in an influential classical journal, "Rheinisches Museum") concerned the historical transmission of the collected verses.