How to Capture Momentary Current Reading on a Multi-meter
You are mistaken &mdash; electrically, the PC sync port functions identically to a hot shoe connection: the camera simply provides a contact closure to ground. In modern cameras, it's actually an open-drain or open-collector output. Any voltage or current is supplied by the flash unit.

But to answer your actual question about the multimeter, if it doesn't have a peak-hold feature built into it already, it isn't something that you can easily add. Get a different meter.

Any further questions on this topic should probably be directed to Photography.SE.