/usr/include/libnitrokey/ is in libnitrokey-dev 3.2-1ubuntu1.
This file is owned by root:root, with mode 0o755.
..
/usr/include/libnitrokey/CommandFailedException.h
/usr/include/libnitrokey/DeviceCommunicationExceptions.h
/usr/include/libnitrokey/LibraryException.h
/usr/include/libnitrokey/LongOperationInProgressException.h
/usr/include/libnitrokey/NK_C_API.h
/usr/include/libnitrokey/NitrokeyManager.h
/usr/include/libnitrokey/command.h
/usr/include/libnitrokey/command_id.h
/usr/include/libnitrokey/cxx_semantics.h
/usr/include/libnitrokey/device.h
/usr/include/libnitrokey/device_proto.h
/usr/include/libnitrokey/dissect.h
/usr/include/libnitrokey/log.h
/usr/include/libnitrokey/misc.h
/usr/include/libnitrokey/stick10_commands.h
/usr/include/libnitrokey/stick10_commands_0.8.h
/usr/include/libnitrokey/stick20_commands.h