To test out merge fields without creating a template and generating the template, you can use the merge field test tool in Admin.
Go to Admin > Document Assembly > Merge field Test Tool.
Using the Merge Field Testing Tool
Choose a template type and a matter to use for the source data and then enter your merge fields between double square brackets.
Here as you can see you have many options. You have the option to just test the merge field code right then and there you can also test a template to make sure you have the correct code and it pulling the correct data.
When testing make sure you select the correct Matter ID to pull from that matters data otherwise you may be pulling the wrong information that you would want.
When testing the code, place the code in the Merge Text box and where you see [[Action_ID]]. Once the code is entered at the very bottom you should see a green button (Generate Output). After that is selected you should see your result where you see "Output".
If you know you have the correct merge field code and are getting "*****" as a result that means the code is correct, which means the data is not entered properly where you are pulling from. Example and address perhaps. You are trying to pull an address from John Smith from Matter 3. However, if you go into John Smith's contact card you see that his address is not entered. Once entered run the test tool again and you should now see the correct address.