The correct syntax would have been /system/health get “cpu-temperature” value if the RouterOS programmers had made one thing uniform with everything else.
But since “cpu-temperature” is not already solved like other sections, [find where name=cpu-temperature] is needed.
So, the needed command line is:
{
:local cputemp [/system/health get [find where name=cpu-temperature] value]
:put $cputemp
}