Firstly thank you for reading my problem.
The problem is that, previously I used SK2 in a virtual machine (Ubuntu 16.04) in my Win10 laptop successfully, now I want to transfer the platform to raspberry pi3 with raspbian system. I did the exact same steps as what I did in the virtual machine, downloaded the AvnetWNCSDK package, pushed the adbkey.pub file to ~/home/XX/.android/ directory, then I entered "sudo adb devices", it says "WNC_ADB unauthorized". I tried kill-server and start-server many times, it was still the same. If I entered "adb shell", it says "This adb server's $ADB_VENDOR_KEYS is not set". I also add an 51-android.rules in directory ~/etc/udev/rules.d/, this problem is still there. But when I plugged SK2 back to virtual machine, it can be accepted and worked well. so I have no idea how to solve that. If anyone could help me. Thank you so much.