No, you can't mine it. It is a Counterparty asset, and all SJCX have been generated and locked already. Some of the SJCX have been distributed in the crowdsale, you can buy them on exchanges (poloniex for example), and when the project launches, those who share their spare storage ("farmers") will be rewarded with SJCX. And if you need some storage in the cloud, you'll have to get some SJCX to pay for it.