here is a doc that explains getting data into splunk using apps or forwarders and whatnot. I'm not sure how useful this is to your question, exactly, but I thought it might help.
Many applications provide a public facing API that you can pull data from. One of my favorites is Zillow. Just google around and you'll find plenty of things that you can load into Splunk.
I'm not sure to have understood your request: do you need logs to learn to use Splunk?
If this is your request see the Splunk Tutorial that guides you to Splunk and gives also the logs to use: