DV360 Site ID (CM Model) is a Dimension in Google Analytics under the DoubleClick Bid Manager section
DV360 Site ID (CM Model) Definition: DBM site ID where the DBM creative was shown and clicked on for the last DBM event (impression or click within the DBM lookback window) associated with the Google Analytics session (Analytics 360 only, requires integration with DBM).
Web Analytics & Insights Google Analytics Dimensions DV360 Site ID (CM Model)