do n't understand what on earth is going on 
(ROOT (S (VP (VBP do) (RB n't) (VP (VB understand) (SBAR (WHNP (WHNP (WP what)) (PP (IN on) (NP (NN earth)))) (S (VP (VBZ is) (VP (VBG going) (PRT (RP on))))))))))
(ROOT (S (VP (VBP ) (RB ) (VP (VB ) (SBAR (WHNP (WHNP (WP )) (PP (IN ) (NP (NN )))) (S (VP (VBZ ) (VP (VBG ) (PRT (RP ))))))))))