In searching for highlighting mode for N3 and gedit, the best I could fine was a blog post from a couple years ago. When writing N3 I am overly cautious about typos, and I could use some indication of syntax errors. So I created a SPARQL syntax highlighting mode for gtksourceview. This will highlight all known xsd, rdf, rdfs, and owl classes, datatypes, and predicates to make creating ontologies in N3 easier.
The file can be downloaded and saved as ~/.gnome2/gtksourceview-1.0/language-specs/sparql.lang. Then the SPARQL mode is available from the View->Highlight Mode->Sources menu.