If you would like to know about the blockchian itself, then you should know C++ because the blockchain was built using C++.
If you are planning to write some code using the RPC nodes and try to perform some operations, your javascript knowledge should be sufficient. There are two javascript libraries available for Hive.
- HiveJS
- Dhive
You can use the above to get started. There are also other libraries like Beem using Python and also another one with ruby that can also interract with the blockchain. But for now I think HiveJS and Dhive should be sufficient to get started as you are already familiar with js.