1. Is there pvp servers in which you don't have to be flagged in game world while exploring to be attacked (like in wow)
2. Is there dueling 1v1 like in wow?
3. Are there any other threats from other players while exploring the game world ?
4. Is all PvP instanced?
1. GW2 isn't WoW so there are no PVP flags to be turned on or off. All servers you see when you log-in are PVE. PVP servers are in a different separated area of the PVE server.
2. No.
3. No.
4. As far as I know, yes.