Craglorn. Most of the content requires a group to do (the delves and quests). Many people also grind out their xp at "camp" spots around the map, so monitor the zone chat for people looking for replacement members for their camp spots.

You can also PVP for XP.

Go back and do any Dolmens or non-vet Dungeons that you skipped. The quests in the dungeons will give you vet xp.

No...
You can get to craglorn by talking to a quest NPC (Star-Grazer Herald) in Mournhold of Deshaan, Elden Hollow of Grahtwood or Wayrest of Stormhaven.