Apparently, some manage to make it to the cockpit (that was before reinforced doors):

> the aircraft suddenly went into a rapid dive nose-first, resulting in weightlessness (zero-g) throughout the cabin. Despite this, the captain was able to fight the zero-g and re-enter the cockpit

https://en.wikipedia.org/wiki/EgyptAir_Flight_990

As long as there is air friction complete zero-g is highly unlikely. It takes a lot of training to set the engines correctly to cause zero g by compensating exactly the air friction

A malicious pilot could injure/incapacitate anybody who wasn't strapped into a seat with aggressive maneuvering. I expect it takes a lot of training for a 'vomit comet' pilot to not toss everybody around like ragdolls, but a suicidal pilot trying to kill everybody wouldn't be gentle about it..

Zero-g is very disorienting to humans. But an experienced pilot could probably handle it and push themselves towards the cockpit.

An experienced airline pilot almost certainly has zero experience moving around in zero-g. Pilots just aren't trained for moving around a freefalling airplane. There are only a handful of 'vomit comets' in existence that could provide such training, and I've never heard of airline pilots being trained in them.

I didn't mean to say that pilots have zero-g training. I just assume that most pilots could handle zero-g enough to orient themselves towards the cockpit. But maybe that's optimistic.