If you have shared a sheet with colleagues, you can view their activity on the sheet to see when they have viewed the sheet over time.

Click on the Activity Dashboard button near the top-right corner of the screen to view the dashboard.

Everyone with access to the sheet will be listed on the Viewers tab and you will be able to see who has viewed the sheet, and the date on which they last viewed it. You can select names in the list to email them using the drop-down list.

Click on the Viewer trend tab to view a chart showing the viewing trend for the sheet

Click on the Comment trend to view when comments were made on the sheet

Click on Sharing history to view how the sheet has been shared over time