In general, many shops in Copenhagen are closed on Sundays. But not department stores and many major retail stores. On Sundays, it's always advised to check the opening hours of your prefered shops. 

Opening hours vary, and department stores and supermarkets usually stay open longer. Outside ordinary shopping hours, various kiosks are open for the sale of tobacco, newspapers and sweets etc. Bakeries, florists and souvenir shops are usually open seven days a week.

These are the most common opening hours:

Monday - Thursday 10:00 - 18:00
Friday 10:00 - 19:00
Saturday 10:00 - 16:00
Sunday 12:00 - 16:00