Think of it this way. The leading edge stagnation point is that place
where there's no 'wind' across that point on the leading edge: a little
higher and the wind flow is upward, a little lower, and it's downward.

Now think about the trailing edge. If you track air across the
surfaces, there will be a place where the upper and lower streams meet,
the flow vector is no longer along the sing, but directly away from it.


It also happens that on most conventional wings, the leading edge is
rounded so the stagnation point can more or less move up or down
depending on angle of attack. On the trailing edge the point is more
nearly a knife edge;