There are two supplementary angles, these are:
SOP and QOT.
Which angle is supplementary to SOQ?
Two angles are supplementary if the measure adds up to 180°, so we need to identify the angles that when added to SOQ, give a plane angle.
It is ratter easy to identify them if you know what you are looking for, in the given diagram SOQ has two supplementary angles, one is:
SOP
Because SOQ + SOP gives the angle SOP, which is a plane angle.
The ther one is:
QOT
Because
SOQ + QOT = SOT
Which also is a plane angle.