How to fix or handle a glitched NPC?

This happens with some quests (and even some world bosses) because of some bugs in ESO's instancing system. Unlike other mmorpgs where you chose one of many servers to create your character on, ESO runs on two "megaservers" (a North American and a European megaserver). This means there are hundreds of thousands -- potentially millions -- of players on your megasever. The game segregates clusters of players into separate instances on the megaserver for obvious reasons (overcrowding, performance, etc).

Furthermore, some quests have phased environments. When you exit a cave or house and the outside world suddenly looks and behaves differently than when you went inside, it's because you've been placed in the next phase of that quest's environment. If your friend hasn't advanced that far, you may not even see him/her in your phase.

So with all this server instancing and quest phase instancing going on, some quests are getting stuck when you try to interact with an NPC or object. At some point, your instance lost track of where you actually are supposed to be in the questline.

In most cases, the easiest way to resolve this is to load into a new instance on your megaserver. Loading into a new instance forces that new instance to re-evaluate your current quests and objectives, and as a result, your previously bugged quest will be workable.

Loading into a new instance can take several re-log attempts. You don't need to restart the whole game. Simply logging out to your character selection screen and logging back in is sufficient. I've had to re-log 4 or 5 times for a quest before it worked, but it does work.

Also, there is a command (/camp) that seems to force you into a new instance, so that may be of help as well.

Since there are no "console cheats" to put it that way as there was in Skyrim i.e., it saddens me to say that there's nothing else you can do besides try to log in again and wait, wait and wait until it resets.

In addition to that, you should always report those glitches so in a "near future" it gets fixed by ESO and people stop getting annoyed by them. Just remember to provide as much information as you can, or else you will most likely be ignored and get a custom answer message. (we've all been there)