how do you know which bonds have a more pie bonding character than the other bond?
and how do you know if it point to one resonance structure over the others?
That's pi as in 3.14 and not pie as in what we eat.
You look at the bond length; for example, a single bond C-C has a bond length of 1.54 A (I think I remember but you should look it up to make sure). A double bond C=C has a shorter length than 1.54 A; thus, bonds that are shorter than 1.54 we might think would have some pi character. I'm not sure I agree with trying to determine which resonance structure points to such and such a bond length since resonance structures really are just figments of our imagination and we draw them in order to try and understand the REAL structure of a molecule. But I won't argue with that==if you have an organic prof s/he knows much more about organic chemistry than I do.