To find out if a particular kernel feature is compiled into the FreeBSD kernel or not, you can use the sysctl command with the kern.features sysctl variable.
For example, to check if the CONFIG_SMP feature is compiled into the kernel, you can run the following command:
# sysctl kern.features | grep CONFIG_SMP
If the CONFIG_SMP feature is compiled into the kernel, the command will output the following line:
kern.features: CONFIG_SMP
If the CONFIG_SMP feature is not compiled into the kernel, the command will not output any lines.
You can replace CONFIG_SMP with the name of any other kernel feature to check if it is compiled into the kernel.
For more information about the sysctl command and the available sysctl variables on a FreeBSD system, you can refer to the FreeBSD documentation and the sysctl man page by running man sysctl on the command line.