The official app is Rejseplanen (English: Journey Planner). Here you can not only see all the connections but the price of the ride with a Rejsekort. You can also use Google Maps, however, Google Maps will not have the latest up-to-date information concerning delays or emergencies which may affect your use of public transportation.
You may have to change the location of your AppStore to Denmark to see the app. If not you can access the website version using this link: https://tinyurl.com/7hxd3f9a