why did i receive a warning about content which content ?

Looks like a comment you've made on Yahoo News was reported as a Terms of Service violation which is more serious than a Community Guidelines violation. The email says Yahoo News not Yahoo Answers. 

The content of your YA questions and answers. This should be obvious. 

Edit: FINALLY! After seeing the screenshot of the email this confirms my suspicions that SOME Yahoo or Verizon employees are tracing the account activities of people who got lots of questions, answers and comments reported.  

You've been warned. The next time this happens your email account may be terminated without notice, NOT suspended, blocked from participating on YA. 

The email is from Verizon Media, NOT Yahoo. It is genuine. Yahoo Media manages Yahoo for Verizon Communications.   

If a real notice, only you can figure that out. If you look at the details of the header, you may find the email is not from Yahoo at all, but a scammer.