i have been playing the dlc for 8 hours and i still cant find were it starts so what quest do i have to start to kill the droagonborn and were do i find it.

Just keep doing the MQ.

and were is that

were do i start the quest

Ask people arounf town if the know Miraak

witch town

You have to go meet the Greybeards first.
You have to get yourself established as the Dragonborn before the cult comes looking for you.
Then fast travel around...you don't find them...they find you.

oops. Sorry. In order to start, you have to at least have recieved the quest from the greybeards to go and get the horn of J. Windcaller. Then fast travel to any town, where you will be approched by 2 cultists. After dealing with them, read the letter and go take the boat

i wish i was tolled that 8 hours ago

There are 3 or 4 topics on it. Sorry you missed them.