In the what3words app:
Open the menu and tap Settings, then Share Settings. Select Latitude & Longitude, and the format you need. Now whenever you share a what3words address, your message will include the location’s coordinates.
Using the online map at what3words.com:
Click the profile icon in the top corner of the screen and select Share Settings. Click Latitude & Longitude, then select the format you need. Now whenever you click Share in the side panel, you’ll see the coordinates in the preview box.