My current character was levelled to 60 using the "Story till 59 then Threads of Fate" trick, and as a result, I never picked up the "Reinforcing Revendreth" part of the Shadowlands Skip before hitting 60. I completed the Bastion, Maldraxxus and Ardenweald ones.

Now that I'm 60, I cannot pick this quest up and so it will forever be shown in Prince Renethal's tooltip:

The reason this quest shows for you is because you see the various quest rewards from the quest which are usable for your character. So in this case, you are missing the Dagger source, which would be rewarded to a Rogue which completes the Shadowlands Skip Zone quest for Revendreth.

The dagger can be also be rewarded to Rogues from various World Quests or other Zone Rewards in Revendreth at level 60.