A man wakeboarding
the person is on the water
The sentence is incomplete, and wakeboarding is generally done on water.
exists e1 x1 x2.(a_topic(x1) & Actor(e1,x2) & v_wakeboard(e1) & (x1 = x2) & n_man(x1))
exists p1 x1 x2.(n_water(x2) & n_person(x1) & on(x1,x2))