Years ago I used to use dry milk in some of my breads. But I got away from doing that for some reason. I was thinking about trying it again because my breads are not rising enough, and have read this might help.
The question is use buttermilk powder I have on hand. Or possibly scald milk and use that? We use skim, or do I need to use "fat" milk for this purpose.
If your breads aren't rising enough, dry milk or milk of any kind won't make much of a difference. You need to solve your fundamental problem.
But if you really want to use milk, any of those will work fine.