Filters are not mentioned anywhere in the
exam objectives, and I can't see any topic there which
requires knowledge of filters, but ...
(a) if you want good knowledge, rather than just passing the exam ...
(b) people have reported questions on, for example,
patterns other than those explicitly mentioned in the objectives.
Same with DTD elements ... the exam objectives mention some explicitly, but I don't think you can take that as being an exhaustive list of the ones you need to know.