Looking at the answer options:

'If the pilot also experiences moderate or severe icing, he/she must make a special air report to ATC. Turbulence alone does NOT need to be reported' --> INCORRECT. Turbulence AND / OR icing that is moderate or severe merits a special report.

'The pilot is experiencing turbulence but must only make a special air report to ATC in case the turbulence is severe' --> INCORRECT. Moderate turbulence also merits a special report.

'The pilot is experiencing severe mountain wave and must make a special air report to ATC of this as soon as practicable' --> CORRECT. See the complete list of weather conditions below.

'The pilot is experiencing mountain wave and must report this to the meteorological office at the destination airport after landing' --> INCORRECT. Too late, this should be done as soon as practicable.

ICAO Doc 4444
4.12.3 Contents of special air-reports

4.12.3.1 Special air-reports shall be made by all aircraft whenever the following conditions are encountered or observed:

a) moderate or severe turbulence; or
b) moderate or severe icing; or
c) severe mountain wave; or
d) thunderstorms, without hail that are obscured, embedded, widespread or in squall lines; or
e) thunderstorms, with hail that are obscured, embedded, widespread or in squall lines; or
f) heavy duststorm or heavy sandstorm; or
g) volcanic ash cloud; or
h) pre-eruption volcanic activity or a volcanic eruption.

Note.— Pre-eruption volcanic activity in this context means unusual and/or increasing volcanic activity which could presage a volcanic eruption. In addition, in the case of transonic and supersonic flight:

i) moderate turbulence; or
j) hail; or
k) cumulonimbus clouds.