I'm going to assume you mean the Google verification code for analytics or Webmaster tools. If you put it in the wrong place, nothing will hapen apart from the fact that the site won't get verified. You'll probably have to re-apply for a new code.
hello dear In search engine optimization, on-page optimization refers to factors that have an effect on your Web site or Web page listing in natural search results. These factors are controlled by you or by coding on your page. Examples of on-page optimization include actual HTML code, meta tags, keyword placement and keyword density.
On page activity is very important as a point of view of Seo. Each and every code is very important whether it is verification like google anlaytics and google webmaster.Each and every code will have to be made on right place.