What types of gametes can be produced by an individual with the genotype aabb?

The answer to this question would be: ab

When doing meiosis to produce gamete, the gene will be separated resulting in a cell with the half genetic material of the parent cells. 
In this case, the organism is having a homozygote recessive gene which means that the gene it has is two recessive gene. Then,  the gamete produced will have the same kind of allele because it paired gene is same.