There are 5 key skills required to be a blockchain developer –
Cryptography

Blockchain is built on various cryptographic algorithms, hence having hands-on knowledge of cryptography is an advantage for a developer
Interoperability

Being able to integrate large-scale applications to drive business solutions and to reduce hurdles faced in workplaces
Data Structure

Deep understanding of data structure is necessary for understanding the relationships and functions operating within the network
Smart Contract Development

In any blockchain based business solution, smart contracts form the base of the network without which it cannot run. Hence it’s a necessity to be well versed in it.
Web Development

Knowledge of designing of DApps (Distributed Applications), ReactJS etc. is the core requirement for a blockchain developer.