The latest cumulative update of Exchange Server 2016 is 10. It was released on 12/6/2018 and you can download from the following link:
https://www.microsoft.com/en-us/download/details.aspx?id=57068
Click the download link next to Exchange Server 2016 cumulative update 10. A new window will open, click the Download button and your downloading will start.
Where to Download the Latest Cumulative Update of Exchange Server 2016?