@Tushar As @danielt mentioned debugging takes place through UART0 most of the times for Neonkey.
Also, the log you are seeing via 10pin connector is actually the log coming from the base board. Neonkey only exposes UART0 (96UART0 according to schematic) interface. So, eventually if you want to debug the firmware running on Neonkey using serial, then you have to see the log using the base board (Hikey 960 in your case) by running a serial monitor on /dev/ttyAMA3.
As far as the software support for this board is concerned, we have just added the Zephyr  board support recently (not merged yet).
Hope this helps!