I will be traveling to Nanjing, China from Germany for 4 days and I would like to rent a mobile WiFi hotspot during my trip. Are there any recommended websites that offer it where I could pick up in the hotel or airport if possible?
You can order a Huawei MIfI device for China and get a China Unicom SIM card to use with it.
An alternative website I found is this one (no affiliation) which seems to offer the service.
Another website which offers this can be found here:
With our China MiFi hotspot rental service, your laptop, apple devices, android phones, or tablets etc. can be connected to high-speed internet at the same time. While travelling in China, your family, friend or colleagues can share this 3G connection up to five Wi-Fi enabled devices.
(Prices can be found on that link)