Witty person travelling by cart (5)
I believe the answer is:
wagon
'cart' is the definition.
(I've seen this in another clue)
'witty person travelling' is the wordplay.
I cannot quite see how this works, but
'person' could be 'wag' (wag is a kind of person) and 'wag' is located in the answer.
The remaining letters 'on' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'by' is the link.
Can you help me to learn more?
(Other definitions for wagon that I've seen before include "Cart; rail truck" , "Wheeled vehicle drawn by a horse" , "On this, one keeps dry!" , "Horse-drawn vehicle" , "Four-wheeled goods vehicle" .)