You could start with https://planet.openstreetmap.org/tile_logs/
In case that you would go through them and manage to identify problematic cases: can you share list?
Either here, contact me somehow or even add cases to https://wiki.openstreetmap.org/wiki/Lacking_proper_attributi... listing?
As a first step I wanted to get at least rough numbers about the scale of the offenses. I will present the proposal either on the legal talk list or write a blog post.
Main of them is that it is barely happening.