Today we have enough technology that an engineer can build a soldier or a merchant (or a farmer or a sailor). We are all familiar with drones and vending machines.
It is important that an engineer not constrain his thinking though. Neither of these replacements does everything a human can do. Sometimes a soldier takes a bullet for a civilian and sometimes a merchant haggles and gives discounts to needy.
Even though these replacements are not perfect they still compete with humans for jobs. We are still a long way from creating a robot engineer. If you want a job that won't be replaced quickly think like an engineer.
We are also closer than ever but still a long way from having a robot doctor or lawyer and will likely be requiring humans for anything resembling a bedside manner or sympathy. Hopefully there will be jobs alongside these artificial replacements for human experts for some time.