See https://electrum-cash-protocol.readthedocs.io/en/latest/
We simply return protocol version "1.4" at the moment, which is what fulcrum also report to Electrum ABC's current request.
This is not exact as we only implement a subset of the commands in that version of the spec, but we do follow the rules for the implemented methods (for instance we don't support some 1.5 additional parameters to blockchain.scripthash.history)