A Proof of Service is a document that your process server with provide to you stating when, where and who was served.
What is substituted service?
If a party appears to be avoiding service of court documents, a request may be made with the court to, instead of personal service (i.e. giving the document directly to the person), that the document be published in a local newspaper, served on a person believed to frequent the person or mailed to his (or her) last known address.