It is a 'dry cleaning system with microfiber brushes', no liquid.

Check for 'Optimum Superior Lens Cleaner' on Amazon or elsewhere. Luckily, it seems to have worked for me also. I purchased a generic cleaner disc off Amazon because 1 single reviewer said that it had fixed their Wii U.

UPDATE: SUCCESS - I took a gamble and it paid off. If that fails, there are allegedly tutorials for replacing the laser, but I think that might be a bridge too far for me. Some people have reported success opening the console and manually cleaning the laser. I have no idea if the ones for Wii will also work on Wii U. There are a fair number of people saying they have used 3rd party tools or hacks to clean a Wii lens, but I've found none specifically about Wii U. But maybe there is one that actually will work and/or cleaning the lens wasn't going to fix that person's problem regardless. Reviews on Amazon for typical DVD/CD lens cleaning discs often contain comments from people that it didn't work on a Wii and/or Wii U. Some people have suggested using compressed air, but never any feedback if it actually helped. The official lens cleaning disk from Nintendo is available on Ebay for ridiculous costs (like $60+). RESEARCH: I've read that a dirty disc lens can't read the more advanced double layer disks, a common problem for Wii consoles, although there are far fewer double layer games for Wii. SOLUTIONS: I'm looking for firsthand knowledge of successful resolution. PROBLEM: Have a Wii U that will read older Wii game discs but not the newer Wii U games discs.

Wii laser lens cleaner