Hi Johan,
First of all: this mailinglist (rdf4j-dev) is really intended for discussion about RDF4J project development - for usage questions we have a separate list, the rdf4j-users group. See
https://groups.google.com/d/forum/rdf4j-users . Not a big deal this time around but could you direct future questions to that list instead?
As to your question: interpreting the owl:sameAs relation (or any other inference based owl or rdfs constructions) is something that requires the use of a reasoner. The RDF4J SPARQL engine does not, by default, use any reasoner. So to get something like owl:sameAs to work, you will need to make sure you use a database configuration that supports (OWL) reasoning.
RDF4J itself does not have a ready-made OWL reasoner, however, something like Ontotext GraphDB might be what you need if you need generic OWL support. If it is specifically only support for the owl:sameAs property you need, there are a couple of possible workarounds without the use of third party tools. One option is to rewrite your query, using a path _expression_. For example, to get back all children of bob (including all resources that are owl:sameAs bob) you could do something like this:
