How do pilots do a preflight inspection of tail-mounted engines? The recently released first part of an Air Clips documentary of a Lufthansa Cargo MD-11 FRA-NBO flight shows in some detail the pilot carrying out the preflight visual inspection of the aircraft (from ~ 6:20 min). As in many other pilots' accounts of these 'walkarounds', the captain states one important aspect is the condition of the engine, including e.g. fan blades, intakes, checks for any foreign objects.

I understand that a major point of this visual inspection is to have the pilot-in-command getting a full picture of the aircraft condition before assuming the final responsibility for the flight. Obviously, the PIC cannot inspect a center tail-mounted engine like on the MD-11 by himself during the walkaround – so when or how is that inspection done for the center engine? I imagine that an inspection of the center engine is just as important as for the wing-mounted ones, prior to each takeoff.
In personal experience, I often look for a step ladder to inspect ground inaccessible engines and control surfaces and I have seen others look at their aircraft from a second story window.

My personal practice is to walk around the aircraft prior to every flight, not just at the first flight of the day, but I often had to make time for that. It may not be common practice. But that is an aside.

Here's the reality. If you are talking about the walk-around that the pilot or flight engineer might do, there are not up close inspections of the elevated engines and control surfaces. The walk-around will look for leaking oil, missing $1500 fasteners or whatever, but one is not checking the dipstick prior to engine start.

How are things inspected?  The manufacturer factors that into the design.

From an operational standpoint, the pilot(s), FE will look at performance during engine start, and make sure that the profile does not deviate from the expected temps, flow, etc.

In summary, if you can't get to it, it is not likely on the walk-around checklist.

Addendum.  At least one company is seeking FAA approval to utilize drones in aircraft maintenance inspection (not pre-flight) processes, which would reduce the cost and risks associated with scaffolding and lifts. As part of their application to FAA, there will be demonstration periods where aircraft are inspected with both methods, and results are shared with the FAA.