I write a character who lost his hearing later in life and, having the financial means to do so, chose to get a CI. I as the writer am not deaf/HoH and I don't actually know anyone who is (and, I mean, it would be kinda rude to ask them for help? I think). Is it okay for someone who is truly deaf in one ear (and has a CI on that side) and the other side about 20% hearing left, to be able to communicate fairly easily? He knows ASL and can lip-read reasonably well.
CIs are often given to people who lost hearing later in life and they usually communicate succesfully with them. Since their brain is already “wired” for spoken communication, so to speak, with a functioning CI they should be able to communicate in spoken language and even use a phone.
Of course, this is variable, but deafened people generally do communicate fairly easily if they have CI. Most of them don’t use sign language, actually, as they prefer communication in their native language, it being spoken language. However, this also depends on age - person who lost their hearing at 15 is gonna act differently compared to person who lost their hearing at 40.
I recommend looking up some articles about how CIs work, when and where they can’t be worn, what are their limitations and advantages, etc.
As for if asking a person is rude... Well, that depends on context and the question. Some people are happy to answer questions about their CIs, some not. You can try reaching out to a CI online group (Facebook is full of them ;) ) and see if anyone would want to help, or ask around here on tumblr.
If you want someone to read your whole story and tell you if you wrote the character correctly, thats called sensitivity reading and its usually a paid position. Its not rude to pay someone for a job. ;)