Missing soul tear?

[Hungry Hank the toilet]

I already did the quest in soul cairn, but i never got the shout to call durnehviir? do i have to go back in soul cairn?

[Alex]

You get the shout to summon Durnehviir when you exit the "arena" where you fought him. Don't just skip through the dialogue, you need to agree to the favor he asks of you. Then, when you actually summon him in Tamriel, then he'll teach you a word of the shout "Soul Tear" as a reward. So, you need to summon him 3 times to get the full shout.
https://en.uesp.net/wiki/Skyrim:Soul_Tear

[Rez Elwin]

Did you talk to him? He teaches you the shout when you speak to him. He should have appeared when you exited the Castle.