Kolbach is a measure of the modification of the malt. It's the ratio of soluble nitrogen to total nitrogen. (Nitrogen = protein). Bags of malt should come with either a "typical" analysis or a batch-specific analysis, and your brew store should have these on file. The exact data varies, but every analysis I've seen gives soluble and total nitrogen, and many will you the Kolbach index.
The long and short of it is, unless you're using a ton of poorly modified wheat malt (like 50%+) or a ton of raw wheat (probably 30%+) a protein rest probably isn't necessary or wise.
To paraphrase Dr. England - "Off-flavors smooth with time. So do mountains. Brew it right from the start!"
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