sudo pkg install py27-sqlite3
Given that nyx is supposedly now written in python 3, perhaps a better
choice would be one of py3[456]-sqlite3, according to which python 3 version is installed, instead of mixing python versions.
Thanks Scott. This crossed my mind when I was writing it but I was unsure if FreeBSD had sqlite3 ports for all the python major/minor versions. Adjusted the message to specify installing for whatever interpreter version they're running...