Use the "Adobe ContextHub" Launch Extension with "Customized ContextHub Data layer" selected. Paste in your schema and save. When you create new data elements that use the Adobe ContextHub Extension you are presented a "Data Item" drop down list of the items listed in your data layer schema.
Yes, completely separate from using or not using Adobe Launch, you should be able to see your data layer in the console. For example, if your data layer is located at window.digitalData you can see a formatted output of it by typing JSON.stringify(window.digitalData); in the console. For other debugging you can also use the Adobe Experience Cloud Debugger - Chrome Web Store extension for Chrome.
p.s. Even though I mistyped Rudi's last name (it's Shumpert), don't forget to mark my above reply as the correct answer to your initial question.