JFK is my favorite airport to depart from when flying to Europe. If your connecting flight through JFK is with the same airline/carrier (for example Delta to Delta) then that time may be enough if flights are on time.
If on the other hand you connect Delta to Air France or KLM then you’ll need more time because each might use a different terminal. These terminals are connected by the free AirTrain however it is on the non secure side. Thus you’ll have to go through TSA at the connecting terminal. It’s a simple process but annoying.
For connecting through Amsterdam (AMS) I select 1 & 1/2 hours as a minimum. Allotting more time is a plus.
For connecting through Paris (CDG) I allow a minimum of 2 & 1/2 hours. Without fail it has always taken me at 1 & 1/2 hours from plane side to the next gate with the bottleneck occurring at the security checkpoint. That’s while using fast track or priority security lines. These have been my experiences.