I've already used an
Organization schema markup for my main site.
Can I use the same for my subdomain (which is a review site)?
Webmasters Stack Exchange is a question and answer site for pro webmasters. It only takes a minute to sign up.Sign up to join this community
Yes, you can use it as long as is the same company and that info is already present in the subdomain.
In addition, don't forget to use ratings & reviews schema in your subdomain.
Google's John Mueller says that schema should generally be unique and implemented on a page which has the schema data as its main focus: https://www.searchenginejournal.com/google-structured-data-unique-page/239507/
It sounds like your main domain home page is the correct place for your organization schema. It shouldn't be reused on the sub-domain or even on other pages on the main domain.