The answer is if the the parents contain the trait to roll their tongues there is 0% chance of the child not being able to. If you mean that the parents do not have trait to rol their tongues then there is a 100% chance the child will not be able to roll it's tongue.
This is because when you are confronted with the term homozygous, the root homo means same. meaning the parents both have both the dominant alleles (the capital letters on the punnet squares that make the genotypes) to roll their tongues and do not have the submissive alleles in which they could not. With no submissive alleles within themselves, they only have the dominant traits to pass on to their offspring.