Right there with you on the Cunningham! I've had my j/22 a couple of years and I've yet to find a good picture of how this is supposed to be setup.
Harken has a deck layout with some photos here. https://www.harken.com/en/support/one-design-deck-layouts/j22/
As best I can tell they have a CL253 Trapeze & Vang Cleat some how rigged as the Cunningham. My rigging that came with the boat also came with a trapeze cleat with roller that had some short lengths of line attached at both ends. I'm not entirely sure how to run it, but on my j/22 there is a cheek block on the starboard side of the mast at the base that seems like it should be involved. I've tried running the trapeze cleat so that the two rollers are working together and the line from the fixed end goes up to the cunningham grommet on the main. That works ok, but I'm not sure it's the correct setup.
