How can i install and use fwknop server without luci.
You can install with
opkg update ; opkg install fwknopd
Then edit the configuration files from SSH session with uci or file editor.
And... Can i compile an C source code of fwknop to my platform, and then run them on openWRT
Why would you do that? Isn't fwknopd available for your platform? What is the output of
cat /etc/openwrt_release ?
Grab a stable release (or the 19.07 RC if you like) for your hardware, log in over SSH, run the commands trendy posted, and be done with it.
Of course you can compile fwknop, but why would you want to if openwrt already offers packages?