In my case I don't really know what ads/landing pages they are talking about
In the email I received they also did not mention the ads and/or the URLs causing the problem. However, yesterday I made some new ads and today I noticed the keywords had 1/10 quality score. So in my specific situation it was easy to find (I keep my vingers crossed that they are talking about the ads I deleted today).
However, when they threat (long term) clients with a ban than they should at least mention the URLs and/or ads in the email.
I have send an email to the Dutch Adwords support and asked some questions about this. I will update this topic when I have new information.