Legal Question in Civil Litigation in California

That someone has filed for bankruptcy is not a matter of judicial notice unless it is reported on in most of the media. The court, however, can be asked to take judicial notice of the papers filed for bankruptcy as though are documents filed in another court system. But since a person can continue doing business while in bankruptcy proceedings, such evidence does not seem relevant as it proves nothing in issue.

Such a document could only be judicially noticed for its existence, not the truth of its contents or its signature. So your question is irrelevant to a demurrer. The document may, however, be completely relevant because the fact that it is on file may require the plaintiff to included something in the complaint to deal with it or "plead around" it. That would, however, be a classic case where the demurrer would normally be sustained with leave to amend.

An assignment of a deed of trust is not required when the promissory note is transferred in California, so the fact that someone unauthorized signed an assignment of a deed of trust is irrelevant to determining whether a nonjudicial foreclosure sale is void.