No train service around noon, when I must go? That’s commonplace (6)
I believe the answer is:
normal
'that's commonplace' is the definition.
(synonyms)
'no train service around noon' is the wordplay.
'no' becomes 'n' (common abbreviation y/n).
'train service' becomes 'oral' (I am not sure about this - if you are sure you should believe this answer much more).
'around' indicates putting letters inside.
'noon' becomes 'm'.
'oral' placed around 'm' is 'ormal'.
'n'+'ormal'='NORMAL'
'when i must go?' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for normal that I've seen before include "Usual, not extraordinary" , "Average or ordinary" , "Standard - well-adjusted" , "Common" , "Unexceptional" .)