Hi, I'm on the quest "the world eaters eyrie", and I've defeated Nahkriin and got his staff but I can't activate the seal, the quest marker is just constantly on Nahkriin. I have no previous save and I've been loading, reloading etc. With no avail. Any help would be appreciated as my game is finished otherwise :-/.

The Staff needs to be placed in the hole at the top of the platform. That will open the portal then just jump into it.

How do I place it in it? It just gives me a prompt to activate dragon seal and that's it. Is there a specific way to put the staff in?

Equip the staff and select it. Same you mount weapons in homes.

I've tried equipping the staff and selecting it and it still doesn't work :-/

I don't know what to tell you then, with staff in hand and selecting the panel on the platform to activate is all that needs to be done. The staff then leaves your hands and inventory and is then set in the hole. The portal opens up and you just jump into it. I'm not sure how to fix it if it's glitched on you.

Ok, thanks for the help anyway its greatly appreciated. I'll try it again later.