how do you know which bonds have a more pie bonding character than the other bond?

Question

and how do you know if it point to one resonance structure over the others?

Answer 1

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.