Duties include turning up on trains (9)
I believe the answer is:
exercises
'trains' is the definition.
(I've seen this before)
'duties include turning up on' is the wordplay.
'duties' becomes 'excises' (I can't explain this - if you can you should believe this answer much more).
'include' means one lot of letters goes inside another.
'turning up' is a reversal indicator.
'on' becomes 're' ('on' can be mean 'with reference to').
're' reversed gives 'er'.
'excises' going around 'er' is 'EXERCISES'.
Can you help me to learn more?
(Other definitions for exercises that I've seen before include "Muscle movements to promote fitness" , "Activities to develop a skill" , "Keep-fit activities" , "Works out" , "trains" .)