How can I tell whether the document should be signed by several people?

Once you have logged in to the e-signing service, you will get a list of documents to sign.

There you will see whether the document has a multi-party signature to be signed by several people, and if some of them have already signed the document.

If you're wondering who the others who must sign the document, you will either see it in the message field, or you will see it in the document itself if you open it.