Meanwhile I found the solution by my self in the troubleshooting section. The answer is here:Why can't I see NOTAMs, TAF or METAR?
SkyDemon relies on an internet connection for certain features such as NOTAM and weather briefing, AIP and AFE airfield plates and flightplan submission. If you cannot access these features it may be the case that you do not currently have a stable internet connection or you are working in Offline Mode. Tap Setup then Communication Options on your iPad, or click the Route button on the toolbar in SkyDemon Plan on your PC to ensure that Offline Mode is not ticked.