You can format your file according to pre-defined rules by pressing Ctrl+Alt+L. Also, press Ctrl+Alt+O to remove unused prefix declarations from the file.
Completion suggestions for prefixed names
Once you declared an IRI prefix and indexed the ontology, you can fetch completion suggestions for corresponding prefixed names with Ctrl+Space or just start typing.
Query SPARQL 1.1 endpoints
It supports all endpoints that comply with SPARQL 1.1 Protocol standard. They are registered in SPARQL Endpoint tool window on the right.
Lookup prefix declarations
It looks up an IR prefix in prefix.cc or in the configuration of the JetBrains IDE. Call the context actions on a prefixed name with Alt+Enter.
Linked Open Vocabularies (LOV) as the fallback option
In case, an RDFS/OWL ontology isn't indexed locally, the Linked Open Vocabularies API is employed to find relevant completion suggestions for prefixed names.
Press Ctrl+Alt+S -> Go to Plugins -> Search for RDF and SPARQL -> Click Install