nvidia-smi --format=csv,noheader --query-gpu=temperature.gpu
but the query can really be anything valid.
The command just sits there consuming 100% of a core without reporting anything or terminating.
The command comes with 384.90 driver in FreeBSD packages.
Its source code is not available, of course, but from libc calls I can tell that it is calling strcmp all the time and also strtok_r and malloc.