I bought a worksharp ken onion sharpener and can't seem to sharpen my Wusthof santoku knife.  Everything I do seems to make it duller(at this point, I didn't think that was possible).  I set it to 20 degrees and follow the guide/manual.  Any ideas?

Worksharp  can fuck your blade pretty fast with an aggressive belt.  Maybe practice on something cheap.

Santoku are better off sharpened at 10-15 degrees rather than 20.

You may not be grinding it all the way to the edge.

Get a black sharpie and coat the cutting edge and make sure you are getting all the way to the edge with the coarsest belt.

You should be able to feel a burr form along the full length of the blade before moving to a finer grit.

There are plenty of good youtube videos.

I use a Kalamazoo 1X42 belt sander to sharpen with and I went to goodwill and bought some cheap kitchen knives to practice on before sharpening my good stuff.

There is a learning curve.

One thing I have learned is to start with a coarse enough belt to avoid overheating the blade getting the angle set and a full length burr.

Depends on the steel.  German stainless is softer and won't do as well with the low angles.

This is my experience.   You're prolly going from a straight grind to a convex grind.   That means you are removing more material profiling the blade before you get to the edge.    Betting you already fucked up the tip.  I hate that sharpener.