Then he assists with a general prompt,  Which piece might go down here? 
( Then ( he ( ( assists ( with ( ( ( a ( general prompt ) ) , ) ( Which ( piece ( might ( ( go down ) here ) ) ) ) ) ) ) ? ) ) )
(ROOT (S (RB Then) (NP (PRP he)) (VP (VBZ assists) (PP (IN with) (NP (NP (DT a) (JJ general) (NN prompt)) (, ,) (SBAR (WHNP (WDT Which)) (S (NP (NN piece)) (VP (MD might) (VP (VB go) (PRT (RP down)) (ADVP (RB here))))))))) (. ?)))
Which piece might fit here?, as he assisted with a general prompt. 
( ( ( Which ( piece ( might ( fit here ) ) ) ) ? ) ( , ( ( as ( he ( assisted ( with ( a ( general prompt ) ) ) ) ) ) . ) ) )
(ROOT (FRAG (FRAG (SBAR (WHNP (WDT Which)) (S (NP (NN piece)) (VP (MD might) (VP (VB fit) (ADVP (RB here)))))) (. ?)) (, ,) (FRAG (SBAR (IN as) (S (NP (PRP he)) (VP (VBN assisted) (PP (IN with) (NP (DT a) (JJ general) (NN prompt)))))) (. .))))