You can install integrationhub enterprise on your pdi, that'll probably give you access to some spokes but the issue is that you will most likely not have access to any enterprise platforms for testing. If you register for azure I think you get some credits you can use to test stuff.
Do you have anything specific in mind? If you just want to understand how to consume APIs just search for public free apis and try to extract some data into servicenow using RESTMessageV2. Then build your own spoke for example. Check out nowlearning and the ihub courses for references
