There are two methods to prove this document.
1. File the print out. It is secondary evidence. If wife refuses to admit this document, then to prove it send summons through the court to the advertisement company and the official from there come with his record and prove the document. He should also to prove that this advertisement has been published by or under the instruction of your wife.
2. To prove the printout as explained by Mr. Prasad above. In this procedure, you cannot prove actually your wife has placed this advertisement.
At the end, I have got my own doubts how much relevant it is to prove this matrimonial advertisement, because my experience tells me that the parties more often than not, rely and sweat out on irrelevant facts and documents.