What how often.
( What ( how ( often . ) ) )
(ROOT (FRAG (SBAR (WHNP (WP What)) (FRAG (SBARQ (WHNP (WRB how)) (ADVP (RB often) (. .)))))))
How frequently did you do it.
( ( How frequently ) ( ( ( did you ) ( do it ) ) . ) )
(ROOT (SBARQ (WHADVP (WRB How) (RB frequently)) (SQ (VBD did) (NP (PRP you)) (VP (VB do) (NP (PRP it)))) (. .)))