When you buy a diary each year, what do you consider important?
Literal
Every-year, diary [object-を] buy time [at-に], what-kind of point [object-を] are-considering-important-[polite-ていますか]?
どんな点 ('what kind of point/aspect') is the question structure. 重要視する ('to regard as important') is a formal compound verb: 重要 ('important') + 視する ('to view as') — a productive suffix for 'to regard as X.'