The reason I ask if that its compiler recognizes the P0.xx pins, but apparently not the P1.xx pins. For example, it throws the error message:
Error: Identifier "P1_00" is undefined in "main.cpp", Line: 9, Col: 12
for this line of code:
Serial pc(P1_00, P0_13);
So, either there's some other way (?) to refer to pin P1.00, or else it would appear mbed doesn't yet support the nRF52840-DK.
There is some support for the nRF52840 DK in mbed, but I don't know how mature it is. I recommend you ask in the mbed forums instead as the mbed port is done by ARM and not by Nordic.