No such Treaty. The Geneva Agreements of 1954 contain no reference to the resumption of hostilities. There was a Declaration by the US made in Washington later, but it is not, to my knowledge, binding on anyone. The Geneva Agreements refer to the Vietnam War. Are you confusing this with the 1953 Armistice Agreement, which the North Koreans have said they already refuse to abide by (quite a few times)?
The text of the Armistice is here
FindLaw: Korean War Armistice Agreement: July 27, 1953