Ever since Blockchain was introduced to the market, security technologists have been busy trying to keep Blockchain transactions secure through distributed networks so people can use bitcoin or crypto-currency as a payment gateway. Hiring managers, especially in the finance/banking industries, are well aware of this technology, so when they ask this question, they are looking for your opinion on how it applies to cyber security. If you have experience working in an environment that uses Blockchain, showcase that experience in a way that makes you stand out from the crowd. For example, use a scenario (without giving away sensitive company information) where you used it, and how you were able to protect web servers and ID systems so the transactions were safe and secure. If you have limited knowledge in Blockchain, show your eagerness to learn the technology, and how your skills would apply in those situations.