How to reduce this RadioGroup Code?
The easiest way would be to define a constant integer array holding the ids:

private static final int[] ids = { R.id.kn1_radio_group, R.id.kn2_radio_group, R.id.pr1_radio_group, /* and so on... */};


And then using the same method as in my answer to your previous question.

However, your naming of these RadioGroups tells me that there might be another structure here. And I also suspect that there is more to your application than what we see here. So what you really should do is to think about the structure of your variables; Should a kn be a class? Should kn4 be an array on it's own, or should perhaps kn be a two-dimensional array (one dimension for the number and one for the letter. These are questions that none of us currently can answer considering the lack of context we have about your application. If you would explain a bit more about What your application is for and what a kn / ap RadioGroup is, then we might help you more. You probably have some reasons for naming the radio groups the way that you do, in which case a different structure than an array might be more useful.

Also, I would like to add something: Why not let the fragment take care of it's own initialization of the RadioGroups? Is perhaps the RadioGroups a part of the fragment's view already? If so, then there is no need to use all these setter methods for it.