"Approximately 5 business days later, you will receive an acknowledgement email, informing you that we have received your application for admission. This notice will also contain your Campus ID Number (CIN). The acknowledgement will remind you about any missing documents needed to complete your application. All documents and other materials must be submitted by the stated deadlines."

You should have received it in an email from the school when you were admitted, if you have for some reason lost or misplaced this email the best way you can get your CIN.

A. (Most Useful Way) Go get your Eagle Card on the second floor across from the bookstore you'll need five dollars and another ID. They will look up your CIN for you and you will end up with a university ID which has your CIN on it.

You are actually killing two birds with one stone with this solution. If you have your school ID then just look at it.