If I perceive an imminent likelihood of an attempt, I'll generally start trying to get a location from them - it's not subtle, they'll know. Sometimes people will give it, other times they resist for whatever reason. For those that resist I will process that feeling that they have and then try again. They may even ask if I'll contact police, in which case I can't lie to them. Ultimately I may _never_ get a location, or I'll have an extremely ill-defined location - it's always up to the caller if that is information they want to give.
clarification: if it gets to the point where I suspect an attempt is likely, or if an attempt is happening, I will start working towards attempting to get location information. The first thing I usually do, however, is help the caller process their feelings to help build trust upfront, even in cases of high suicidality. Speed is of the essence though in certain circumstances.