With your version it might be graph.admin.clear() or graph.clear()
in my version has been ready graph.clear(); it's for truncate the data grakn, not for delete keyspace.
can I got your grakn version?
We recently made a release of 0.13 you can download it here
Thanks @filipe form grakn 0.12.0 I have some example from here .can I got the example 0.13 ?I think the code its differerent.