it looks like the place where the internal power connector should normally be isn't populated. During the manufacturing process those "holes / pins" in the PCB usually get soldered shut when there's no component there - that's why those "holes / pins" look blocked
As you bought a NUC kit with a case it could be possible that those are intentionally left unpopulated.
What kind of powersupply do you want to use for your robot project? Maybe you could get a cheap 3rd-party powersupply and salvage the plug&cord of that to connect to the external power jack of your NUC.