I searched the web for what ISO 8601 is, and seems to be an ISO standard for date‑time format according to locales.
I don't know how it directly relates to Unicode neither why someone directed you here, but may be a guess is that one wanted to instead direct you to a specific part of Unicode activities, which is the CLDR.
Unicode CLDR stands for Unicode Common Locale Data Repository.
An entry point on the topic could be this web location:cldr.unicode.org
You may also access the CLDR data and materials in the dedicated subdirectory of Unicode/Public, here:Index of /Public/cldr/
Hope this will help a bit :)