I'll assume you're not getting them prescribed other wise you would just look on you're bottle for dosing instructions. What do want to take neurontin for ? I know what it's typically prescribed for. With that med can come some pretty funky side affects but I'll only mention one. It turned my passive by nature brother into a raging maniac. They call that side effect "irritability" but it was much more than that. They gave him an alternative that worked well for him. I'm not really comfortable recommending a dosage after what I saw with my brother but maybe someone else will.
you should ask for doc about this because some drugs can react badly with suboxone i dont think neurontin is in this category but wanna make sure. Also if your going to take it anyways, just start with 1. Always better to be safe than sorry.