How do you sue something that is decentralized?

Possible trademark infrigement is one example.
https://www.cryptonewsz.com/oracle-sues-blockchain-startup-for-trademark-infringement/37358/

Other examples may include liability, intellectual property and data protection.
https://www.dlapiper.com/en/us/insights/publications/2017/06/blockchain-background-challenges-legal-issues/

And finally, does one's digitial assets qualify as a security?
https://www.coindesk.com/investors-suing-ripple-cite-sec-guidance-to-argue-xrp-is-a-security

These examples could apply to the blockchain's parent orginization or to those maintaining and managining it.