I would love to be able to predict protein folding and interaction from DNA sequences. That would be the most amazing achievement I think, since you can potentially use that to design proteins to carry out specific functions (potentially leading to many potential cures and understanding of diseases). At the moment, DNA is much easier to study than proteins because we do not know how they fold / interact with each other, despite they are the major molecules that carry out cell functions.
I would love to unveil what exactly this major mutation in a gene that causes blood cancer is doing to the cells to turn them cancerous. That way I could really help develop new therapies for patients.