I believe I've figured it out. I selected "Automatic reference.." and then picked the data page (is this a data page?: "SAE-HRServices-Data-Position") I wanted to lookup from. (not sure if I'm saying all that correctly).
I believe you are referring to the "Auto Populate a Page Property" exercise. Please let me know if this is not correct.
The information in the Approach section is not correct - an oversite when the course was updated from Pega 7.1.2 to 7.1.6. Although the approach is incorrect, the instructions in the solution PDF provided in the self-study exercise is correct.
...Open the Position property and select Refer to a data page in the Data Access Area. - is incorrect and should be:
...Click the Open Position Details edit icon (looks like a gear or cog wheel). When the Data Type details form appears, select "to Automatically source data at runtime." This will open additional fields. Use: