The realtor must disclose what information he/she knows. However, if s/he doesn't know, there is nothing to disclose. Zoning differs from town to town and from time to time. It is always best to look into the situation yourself.
As a buyer, you would be wise to go to the City Hall and review all the permits and information on the property. If you have a specific zoning question, it would not hurt to put a call into the inspectional services of the City or Town or look it up in the City/Town ordinances.
Good questions to ask are:
1) Is the neighborhood under any Historical restrictions?
2) Is the property under any special permit restrictions?
3) Is the property currently a conforming property under all current zoning rules?
If the answer to that question is not known for the specific property (i.e. no one has tried to do anything there in a long time, so no one really knows) then ask general questions to see if the property would trigger any conditions.