How to show current date and time in dashboard?

1. show current date and time in Text widget
   
2. show current date and time in any widget title.

How to show current date time in Text widget

1. Create Today() expression as shown below
   
   
2. Drag and drop the Text widget and use the expression in it as shown below
   
   

3. Preview/ View the dashboard. Now the time will be shown on the Text widget.
   
   

How to show current date time in widget title

You can also show date time in widget title as shown in below image. Follow the steps mentioned in this link.