Replacing a missing capacitor
Since capacitors are not typically marked, the only way to find the value is to measure them.

You'll have to get a meter that can measure capacitance1, take the corresponding capacitor off of the good board, measure its value, and then purchase a replacement that's the same size and value. Solder both capacitors back onto their respective boards.

BTW, even without a scale for measurement, that looks a lot more like 0805 to me than 1206.



1 There are plenty of cheap LCR tester kits on the market that can do this.