Spot head of zoo taking computer studies (3)
I believe the answer is:
zit
'spot' is the definition.
'head of zoo taking computer studies' is the wordplay.
'head of' indicates taking the first letters.
'taking' means one lot of letters go next to another.
'computer studies' becomes 'it' (Information Technology).
The first letter of 'zoo' is 'z'.
'z'+'it'='ZIT'
(Other definitions for zit that I've seen before include "Spot or pimple" , "Spot (colloq., mostly US)" , "Pimple (US)" .)