Thank you for your good question.
I see this 404 Error for Help topics presented in Pega Community very frequently now.
This is a regression that seems to have cropped up since the Pega 8.5 GA release.
From Pega Community > Support > Resources > Download System Help Files > Version 8.3 > Dev Studio Help, you can search for “Queue for Processing method” and find the Help topic you need.
We will also continue to report instances of this Pega Community bug and watch for the bug fix.