Filtered Push Annotation Example SPARQL Endpoint
Here is a paper about annotating data using the Open Annotation Ontology. For convenience, a single zip file. wraps all the ontologies and examples cited in the Supporting Information section of that paper.
Some other SPARQL Competency Questions for data annotation are here. Cut and paste one at a time or you will provoke a SPARQL error. Don't forget to include the PREFIX lines in the query.