Civil Litigation

It's not clear who's a defendant and who's a witness here, since you said "named on a complaint" but then you said "named as a witness." It's not clear is anyone's been ordered to appear anywhere. You'll know if you have to appear somewhere and when because you (or your lawyer if you have one) will get served with a Notice to Appear (if you're a party to the lawsuit) or with a Subpoena (if you're a non-party witness). If you don't get served with those documents, you don't have to appear anywhere. If the plaintiff makes someone appear and they've got no knowledge, that's the plaintiff's problem, but whoever is properly served still has to appear.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.