Neither domain name option is a very good idea. I'll explain why in a second, but first I'll answer your actual question.

Although there might arguably be some slight advantage in having an exact-match domain of the form Name.TLD as opposed to a domain with additional keywords alongside the name, that advantage is probably negligible. Google algorithm updates, as I understand them, withhold that exact-match-domain advantage until a website has many other reinforcing signals of authority. (Their goal has been to downgrade spammy, low-quality websites.)

Whichever domain version you might choose, Google will find the brand name CUJO mentioned all over your actual website and in the referring links. Those signals will be plenty for search engines to pick up on and hence plenty for SEO, and I'd expect them to overshadow the tiny difference between the 2 domains.

Your choice shouldn't be based on SEO. Stop trying to please search engines, and start paying attention to your actual human audience. Really, your decision ought to be made based on the memorability and first impression of the domains. Is the extra keyword in .COM better than a name without that extra keyword in .IO? For humans, that is.

Either way, you'll run into competition from CUJO.com. And that's a potential problem.

Another problem would be pronunciation ambiguity. Spanish and English speakers will see the name very differently, based on that "J". Spelling isn't altogether clear either – Koojo, Kujo, Coojo, Cujo?

The main problem I see, however, is that Cujo is a murderous dog in a Stephen King novel. Since most searches for Cujo will aim at that meaning, your site will be perceived by Google as usually irrelevant in comparison with searchers' intentions. And that doesn't help SEO.