Can you find a clip's ISO in FCPX

Is this metadata available in the native software?

Unfortunately video "EXIF" data is not standardized the way stills are. Video cameras often use proprietary and undocumented data structures to record this. Thus deciphering it requires reverse engineering and the metadata is subject to change without notice.

Probably the best way to attempt extracting that info is using the command-line tool ExifTool, which works on both video and stills. For some video cameras it can extract a fair amount of info from the files, from others not so much: www.sno.phy.queensu.ca/~phil/exiftool/

Some camera manufacturers may have vendor-specific software tools to decode this. Some of the tools may be publicly available whereas others may be for internal support or product development.

A still camera can record EXIF, IPTC and XMP metadata for each image. But with video cameras, various exposure and other parameters can fluctuate over the span of a clip. What you ideally want is not the parameters at the start of a (say) 15 minute clip, but the parameters of the clip range of interest. This would require writing all that frame-unique metadata 30 or 60 times a second, or some protocol for sample frequency every x frames. I don't know which (if any) cameras do this. Maybe a RED camera or others which record lots of metadata in sidecar files do .