Via DVB-T (also not DVB-T2) it is not possible to receive Sky programs.
This is via satellite connection, cable connection (e.g., cable Germany, private cable network operators), IPTV (e.g., telecom).
Otherwise you can book Sky-Ticket as an online contract: https://skyticket.sky.de/home/index/
Before booking any Sky Packages you should have informed yourself about the way you receive your TV signal
Maybe your cable signal is already included in your monthly rent? Otherwise you can ask the owner, if it would be possible to install a small Satellite Equipment outside, but I suppose that you will not get such an autorization, as you have already cable in your appartment. However, such a question will cost you zero Euros