It happened around 2.20am, on Monday April 2, in Lemons takeaway on Keighley Road, Skipton.
The victim; a man aged in his early twenties, suffered a deep laceration to his lip and a temporary loss of consciousness.
He was given stitches for the wound at Airedale Hospital later that day.
Investigators want to trace a man who was with a woman at the time of the incident, as he may have information which would assist the investigation.
It is believed there were a number of people in the takeaway at the time and police are appealing to any witnesses or or anyone who can identify the man police want to speak to, to come forward.
Call North Yorkshire Police on 101, select option 2, and ask to speak to Michael Haydock. Or email [email protected] or call Crimestoppers on 0800 555 111.