For your full build example is that the build order you're saying to do? Because seems a bit odd to end with Blade of the Ruined King.

Also for fighting Nocturne you should still rely on your E because you can make it go off manually sooner before Nocturne puts spell shield up. You will normally win a face off against a Nocturne if you have ult unless he is way ahead in exp and gold or is building full life steal, even then you got a chance. Nocturne's spell shield relies a lot on prediction which means it is really easy to bait it out of him. I am really good at Nocturne and have noticed that even when I have like 18 kills and almost no deaths that fighting Warwick is a challenge. Warwick is the superior duelist which makes sense because it's a fighter tank (Warwick) vs a fighter assassin (Nocturne). I think difficulty for it should be upper yellow, not red. Just my opinion, I play both champions.

Jax and Wukong are actually very good against Warwick if the players are good. Their kits counter Warwick a lot. High burst, jax has CC and can tank. Wukong has great abilities to burst you and then get away, rinse and repeat. Both have kits that prepare them to fight something like Warwick. However Jax is less a challenge later in the game when Warwick is truly strong but at that time a good Wukong is a nightmare for Warwick.

You suggest a mercurial scimitar against heavy ap but not wits end? Its still a godtier item on warwick and if you need mr and dont want wits end you can still get maw of malmortius. Cant understand that recommendation but maybe im just a pleb that doesnt know whats good?