I'm stuck on a question: For the example on my homework, they're using "Mrs Light", "Mr. Light", and "the Baby at the Light's house". The Phenotype (blood type) for "Mrs. Light", "Mr. Light" and "the baby at the light's house" are all "A". And the Genotypes for "A" are IAIA or IAi. So what if I get a question asking to show the possible blood genotypes of a child born to the Brights? How would I show that using a Punnet Square? 

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Assuming you mean the possible genotypes of the child born to the Lights, not the Brights for which we know nothing you can try three different Punnett squares.  Number one square has IA  and IA for the top; IA and IA for the sides.  Thus all four squares would be IAIA, homozygous dominant with a phenotype of type A You could have the top the same and the side rows be IA and i since this is also a genotype for a type A blood person.  In this case you would end up with three squares of IAIA and one square of IAi, but both of these are type A so it meets your description. Another square might have IA and i on top and IA and i on the side rows.  Both of these parents are type A phenotypes In this case you could get IAIA or two IAi or even one ii which is a type O phenotype while all the others are type A.   There cannot be a type B, IB allele in any of the parents because it is codominant with IA and would produce type AB phenotoype blood, not type A or type B.  Therefore there cannot be any type B allele in the offspring.