Educates boy wizard, one seen on King's Cross platform? (12)
I believe the answer is:
'one seen on king's cross platform?' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'educates boy wizard' is the wordplay.
'educates' becomes 'trains' (training is a kind of educating).
'boy wizard' becomes 'potter' (Harry Potter).
Can you help me to learn more?
(Other definitions for trainspotter that I've seen before include "anorak" , "Boring person" , "Gricer" , "One interested in engines" , "Nerd" .)