There are several nutrition certifications that you can acquire that are accepted as CEUs for different certifying agencies. They go through a thorough scope of practice as to what you can and can not do. www.precisionnutrition.com is an excellent one.
Another resource is to looking into becoming a health coach. The certifications tend to cover nutrition as well as behavioural change. As you know, its not enough to know what information to cover with a client, but how to help them make the necessary changes to help them reach their goals. Many of the top ranked health coaching certifications also cover scope of practice. www.wellcoaches.com or www.IIN.com are two well respected health coaching certifications.
I think it is increasingly important to be able to discuss nutrition within our guidelines to help our clients reach their goals. To simply not engage in the topic can leave our clients helpless and does a disservice to them. That is not to say that we should be providing specific micro-nutrient meal plans for various disease states, but there is a lot that we can discuss when it comes to macro-nutrients that will help a client get from point A to point B in achieving their goals.