I can't find the first word of Durnehviir's shout? Can someone direct me there?

I believe he gives it to you in the Soul Cairn. Mine is bugged though and won't call him.

My journal still shows I haven't learned the first word, how do you return to the Soul Cairn? I remember it's supposed to be possible but I can't remember how.

Durnehviir gives you effectively two shouts - one he gives you in the Soul Cairn, and that allows you to summon him - look for "Summon Durnehviir" in your shouts. Every time you summon him in Tamriel, he'll teach you a single word (up to three - "Rii" "Vaaz" and "Zol") for the shout "Soul Tear", and those words are the ones being referenced in your quest journal. The "Dur Neh Viir" words needed to summon him have already been given to you in Soul Cairn.

Durnehviir's shout is special in that it works like a regular Conjuration spell - i.e. it will not cast if you aim too far away. You need to find a nice flat area in Skyrim and shout with your crosshair pointing close to your feet to summon him. Was kinda confusing at first b/c you could summon Odahviing by shouting at the sky

You have to find an area for him to able to land, and shout towards the ground. It tends to work really well in front of castle Volkhair.

He gives you all 3 words to summon him the first time you speak to him. You have to unlock the 2nd and 3rd but they should be there if you have the call listed in your shouts. I didn't notice this and couldn't get him to come either.

Oh and you can get back to the soul carin in the vampire castle. If you exited in Serana's mom's lab where the entry to the soul carin is, you should have a balcony spot behind the castle on your map.

If you have managed to get all three words to summon him, unlock them. Find a large flat area that is solid ground, then as what ever it is is bearing down on you, panic! Look at your feet and shout holding the button for ages, while cursing that stupid dragon, usually works for me. I swear sometimes that dragon is just too fussy about where he is going to appear, and now even when he appears he says a few words and vanishes on one of my characters.

You might need to quickly move out of the way trying that method, before some stupid dragon appears right on top of you.

Anyone know if the Summoner perks work with Durnehvir?

It's a shout not a summon so I don't think it will level conjuration or use conjuration perks