Normally, you cannot observe J-J splitting when the intervening bond is equal to or more than 4 between 2 types of protons.
However, you can still observe that splitting in aromatic and vinylic molecules.
For your case, theoretically, the proton C is multiplet, but there is one more thing.
The proton C is aldehydic, the J-J splitting is relative very small, you can only observe the splitting by expanding the signal (except for very high frequency NMR spectrometer). Why it is small? I can only tell you that it is affected by the carbonyl group.
Therefore, you can observe the J-J splitting of proton C mainly by the adjacent proton (it is very small also), and sometimes, you can only observe 1 peak for aldehyde molecules.