Hi there,
I have just used this extension for the first time and it worked first time.
You have to ensure that you setup an extrafield group in K2 with an extrafield set as a textfield.
Make sure that the category which you use is configured to use the corresponding extrafield group.
Once you have that setup, then in the K2 Hotspots plugin, select the corresponding k2 category and make sure to set the Address to pick the correct extrafield name you setup.
Now, in the K2 item, in the corresponding category, make sure to add the address details in the extrafields tab.
Now make sure that the component settings are set to display the K2 content, you should see that there are now items in the Hot Spot Locations
Hope that helps.