Simply use /r switch with shutdown command to reboot windows server using command line. Here are various examples of shutdown command.
Restart local system
c:/> shutdown /r
Restart local system with forcefully close running applications using /f command line switch.
c:/> shutdown /r /f
Restart remote system by specifying system hostname with /m command line switch.
c:/> shutdown /r /f /m \\REMOTE-PC
Add a comment as reason of rebooting system suing /c command line switch.
c:/> shutdown /r /f /m \\REMOTE-PC /c "After Installing Software"