How to hit a hermit?
 

I can target him with /tar a_hermit but nothing seems to be able to hit him because I can't see him....

Supposedly saying "i am here to kill you", causes him to run at you and attack.

There's a crack on the right side of the door you can shoot an arrow or cast through. Alternatively, yeah, you can utter a phrase about killing him that you can find on the wiki to lure him out (you may have to be very close to him).

You have to stand next to his house (inside the wall of his complex). To get the /say to work you have to stand at the back of his house, where the chimney is ... but first you have to target him.

You should be able target him from anywhere outside the house (not just the chimney) with just this: Although:

should work too.

If that doesn't work maybe someone just killed him?

I literally was doing that camp yesterday so I'm certain the above works.

I recommend for such things as there is always some player nearby that decided to do the non-social thing and start their name with an 'a'.

I always clicked on him through the crack on the right of the door. Get up close to the door and you can click inside the house and usually it gets him. U is the key to target whats in front of you l think that worked a couple times too

Targeting is easy with the command line I just cant see him.

You don't have to: just target him first, stand by the chimney, and say the phrase.

Alternatively you can also cast on him, shoot him with an arrow, send your pet in, etc.