Edit: Those instruction are partially outdated for KSP 1.8. Have a look at the post following this one and specifically this one if you are on Windows.
As we all know debugging plugin in KSP is mostly done with endless spam of Debug.Log or a bunch of custom windows we have to build. We also have angavrilov method but it require to recompile the whole mono and is a bit scary. So here is the result of a couple of days of experiment on my side to get a simple method working.