We as guards know what a drivers protocol is in an incident, so, while he's following that, we should be ruling out the obvious- passcom, emergency exit, REC. If nothing forthcoming, quick buzz cab to cab and wait. If no reply, and assuming train is not derailed, general pa about checking why we've stopped and then quiet walk to front cab. Knock on and take it as you find it.
Trickier when in train but I generally make to nearest door panel, listen for cab to cab squeal on pa and key on to check for passcom. Wait a bit, buzz, etc.
In return, I've had drivers walk down trains to check on me if I've not released or closed the doors in a reasonable time frame after arriving at a station.
As others have said, we're a team and we're both aware of what the other has to do, and how long it should take. Anything after that, time to start checking. You get to know how people work and whether something is normal or not for a particular driver too. Everyone has their quirks.