The Crown said there would also be forensic evidence given that the blood on the knife was from the victim.
Ms Synnott could not confirm what the substance, in which the print had been left, was, but said it would have had to be damp at the time.
She was asked to demonstrate how the knife could have been held - using a ruler as a mock weapon - to produce a print like the one she found.
Ms Synnott held it in a conventional way and showed it to the jury.
Crown prosecutor Natalie Walker said the defendants had begun an affair months before Davender Singh's throat was slit.
After 130 calls and more than 1000 text messages in the space of three months, it is alleged their respective partners discovered the relationship and electronic communication between the couple ceased, forcing them to exchange notes at work.
Ms Synnott also examined those notes, found in Gurjinder Singh's car and the Penrose factory where they worked.
She told the court there were prints from both accused on various pieces of paper.
On the night of August 7, it is alleged the victim picked up his wife from work and they pulled over on Norman Spencer Drive on the way home.
The Crown said they could be seen doing so on CCTV, which also depicted another car pulling up behind them a couple of minutes later.
Ms Walker said Gurjinder Singh was the driver of that vehicle and stabbed Kaur's partner to death before making a swift getaway.
The trial continues.
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