I have xdrip4ios but I think Shuggah works the same way.
You need to use the Calendar complication on your watch. create a calendar on your iPhone called xdrip. In settings in shuggah set it to create Calendar events and use the calendar called xdrip. Then find a watch face which shows the Calendar and the readings will appear.
it’s all detailed in the help guide.
on mine here I have the calendar complication at the bottom.