Pet-owners always call their own pets 'he' or 'she' - never it. They'd get quite upset if you referred to their beloved dog, cat or rabbit as an 'it'. To avoid causing offence, you need to listen carefully and ask clever questions to find out what sex the animal is, then follow the owner's cue and use 'he' or 'she' accordingly. The same applies to people's babies.

If you are talking about someones pet, usually you say HE/SHE. If you are talking about a random pet (owner unknown) you might say IT. "Did you say that dog at the store? Yes, I saw it."

If the animal is a pet, and you know its sex you refer to it as 'he' or 'she'.

You have to use "it".

I would ask if it's a he or a she but I wouldn't call it IT. For example if I didn't know the sex I would say that's a lovely dog Or what's your dog's name?