Hi!
If you were asking about triple filtering on RDF data that you already have (not "filtered generation" of new RDF), then this is not something that WDTK aims at (since WDTK does not read RDF data in the first place). However, you can often achieve this with grep if the RDF data is in ntriples format.
In simple cases - like just finding one predicate - probably yes, but in some cases statements can span multiple lines/clauses, etc. And, we don't actually have a dump in ntriples format, only in Turtle - which is not super-greppable. We could probably produce one manually but I wonder if we already have a tool that deals with a lot of this stuff... Not reading RDF may be a problem, I though it could read RDF too, not just write. I wonder if it's worth adding, for other use cases too. But I'll think more about it.