My perennial recommendation for this sort of thing is the Kershaw CQC-6K. Either the D2 or 8Cr14MoV versions, your choice. Normal people probably want the 8Cr one. Like all of the Emerson derived wave openers, it can be snapped open automatically when drawn from the pocket by way of a hook on the back of the blade. Drawing and opening it are not separate actions, or at least they don’t need to be.

I hope your friend knows what they’re doing re: trying to use a knife for self defense. I suspect they don’t. As others here have mentioned, doing so is not for the uninitiated. It doesn’t work like it does in the movies. Pulling a weapon escalates any situation and should not be done unless you’re prepared to use it immediately and are justified in doing so. Pulling a knife and waving it around in front of punks on the street is, let’s say, very unlikely to produce the results you want. Especially if you are not already of a stature to kick their asses to begin with, even without the knife.

A Leatherman tool and a can of pepper spray may be a wiser purchase.

In case anyone asks, my scale of self-defense options places a pocketknife squarely at the bottom well behind guns, bear mace, tactical airstrikes, swords, polearms, keeping a Doberman in your pocket, or just not putting yourself in sketchy situations to begin with.