In the what3words app:
Open the menu and tap ‘Settings’, then ‘Share Settings’. Select Latitude & Longitude, and the format you need (decimals, degrees, mins & secs etc.).
Now, whenever you share a what3words address, the Latitude and Longitude will be included.
Using the online map at what3words.com:
Select the square you need, then click ‘Share’ and ‘Customise Share Settings’. Toggle on Latitude & Longitude, then select the format you need (decimals, degrees, mins & secs etc.).
Now, whenever you click ‘Share’ in the address box, you’ll see the location’s coordinates in the share preview.