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 moved towards the table and assisted with a general prompt. 
( ( ( Which ( piece ( might ( fit here ) ) ) ) ? ) ( , ( ( as ( he ( ( ( moved ( towards ( the table ) ) ) and ) ( 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 (VP (VBN moved) (PP (IN towards) (NP (DT the) (NN table)))) (CC and) (VP (VBN assisted) (PP (IN with) (NP (DT a) (JJ general) (NN prompt))))))) (. .))))