This is an important question to be objectively answered by you before starting on the journey to having your book published - by anybody - even yourself. Editors who consider acquiring non-fiction books generally call this the "target market". Agents will look for the same answer from you. Considering the answer to determine the potential size of the "target market" and how wide or narrow it is becomes hugely important for a variety of reasons - like a) will that market dominantly look to buy the book in a retail store or a specialty environment like clubs, associations at speaking engagements? and b) what data can you provide showing the size and location of the market? and c) do you have the credentials to write for the market? All vital stuff.
A number of you took me up on my offer to evalaute your credentials at no charge. The same offer is made in helping you assess your answer to the question "who will want to buy/read your book?