Delete: The alumnus can read and write (10)
I believe the answer is:
'delete' is the definition.
'alumnus can read and write' is the wordplay.
I cannot really see how this works, but
'alumnus' could be 'ob' (old boy, as in an old private school pupil) and 'ob' is present in the answer.
The remaining letters 'literate' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'the' is the link.
Can you help me to learn more?
(Other definitions for obliterate that I've seen before include "get rid of" , "Efface, blot out" , "rub out" , "Wipe out" , "Utterly destroy" .)