I am not sure what you are asking. An easement is a non-possessory interest in the real estate of another. An ability to walk across another person's land is an example of an easement. What I think you may be asking is whether a fence you wish to erect would interfere with the easement rights of another. To find that out, you need to check the public record and see whether any easements exist on your land and check your boundary lines with a survey. If there are easements to which a fence would interfere, then you may need a lawyer to explain the various issues to ypu
The answer to this question does not constitute legal advice nor does create a client relationship with the attorney answering this question. For more specific advice regarding your situation, please consult your lawyer.
Attorney Dinan has it correct where easements are concerned. Search your public records and check for any easements on record, but also consider that your neighbors may not be talking about an easement, or having access restricted to an easement.
There are also property restrictions governed by local ordinance and local building departments that dictate how close your are able to construct various items to your property's boundaries called set backs. A shed or garage may have a different set back than a fence, a cyclone fence (chain link fence) may have a different set back than a privacy fence. After determining if your property has any easements on record, check with your local building department to see if the fence would violate any local set back ordinances.
This is most likely an ordinance issue not an easement. Most city will have ordinances indicating how far from a property line you can erect a building and such. They will also have ordinances regarding fencing. Check with your city government about these restrictions. Often you need a permit anyways.